When does cold and flu season end?


Guide to Parents and Teachers to Prevent the Spread of the Flu

The span of time in which the influenza virus is at its most contagious is widely referred to as “flu season.” This period generally occurs during the colder months of the year. During flu season, health professionals will often begin to distribute resources that are designed to provide people with flu prevention guidelines. Some common examples include basic literature that describes the benefits of flu vaccinations and diagrams that depict the best hand-washing techniques for preventing flu infections.

Influenza (commonly known as the flu) is an infectious respiratory illness that is caused by the flu virus. This disease can cause a host of uncomfortable and painful symptoms:

  • Nausea
  • Fatigue
  • Fever
  • Sore throat
  • Nasal congestion
  • Headaches

People who are infected with the flu often experience some combination of these symptoms, if not all of them, as the illness progresses. Depending on the level of health a person has before contracting influenza, these symptoms also have the potential to cause complications that can lead to death.

  • Experts within the medical community currently believe that this virus is mainly transferred via small droplets that are spread when people infected by the flu speak, cough, or sneeze.
  • In addition, the high frequency at which most people interact with other people on a daily basis makes it nearly impossible to avoid every single infectious particle.
  • Therefore, outbreaks of the disease can spread quickly—and often do.

Research performed by the Centers for Disease Control and Prevention (CDC) in 2016 has shown that a majority of US citizens catch the flu at least once per year. Fortunately, many public and private organizations work to limit the impact of the flu by actively promoting influenza awareness throughout the United States.

The government and other private health entities may even run advertisements that aim to alert people that it is time to get a flu vaccination. Still, many people may not yet be aware of how flu season can impact communities. Therefore, it is critical that people who are unsure about flu season take the time to develop a more in-depth understanding of how flu season works. In doing so, they will likely enhance their ability to protect themselves, as well as their loved ones, from influenza this season.

When Does Flu Season Officially Start?

There is no fixed date for the start of flu season. Instead, flu season is characteristically marked by the winter months coming in and the weather cooling down.

  • Influenza may circulate lightly through populations throughout the entire year, causing a few infections, but winter weather triggers the flu to be exponentially more active.
  • Although the medical field has not yet identified exactly why flu viruses are more active in the winter, cold weather is universally believed to be a primary catalyst for the start of flu season.
  • Once there is a significant spike in the number of influenza infections occurring throughout the population, the CDC officially declares that flu season has begun.

As this season progresses, the CDC constantly tracks, collects, and analyzes data related to flu infections. This allows it to identify trends in when and where the flu virus is being spread. Based on these trends, the CDC can forecast when the virus is at its peak level of infectiousness and inform at-risk community members to take extra precautions.

Flu season typically falls sometime between the start of fall and the end of spring. For the past three decades, flu activity has peaked at some point between the months of October and February but always tapers off by April.

Peak Months of Flu Activity

Here is a breakdown of the “peak months of flu activity” over a 34-year period between 1982 and 2016:

  1. February was the peak month for flu activity in 14 of the 34 flu seasons, making it the most common month for peak flu activity.
  2. December followed February, with the highest flu activity in seven of the 34 flu seasons.
  3. March is third, with flu activity peaking this month in six seasons during the 34-season period.
  4. January was the least common month to facilitate peak flu activity, with the flu peaking this month in only five of the 34 flu seasons.

Groups Who Are at High Risk for Developing Flu-Related Complications

  • Children younger than five, especially those below age two
  • Adults 65 years and older
  • Pregnant women
  • Nursing home residents and the patients of long-term care facilities

Even the CDC cannot precisely predict when and how flu season will start each year. But by monitoring influenza data across the country, the CDC can provide resources that US communities can use to mitigate the effects of particular flu outbreaks.

Tips for Parents on Helping Prevent the Spread of the Flu

Once flu season has begun, parents must teach their children how to prevent themselves from getting the flu. This is especially important for children who suffer from long-term medical conditions, such as asthma, diabetes, or neurological disorders. These and other conditions may complicate a flu infection, necessitating hospitalization.

The same precautions must be taken for children who are younger than the age of five, especially for children below the age of two. Flu infections have the potential to result in extreme discomfort and even death, so it is important that parents take action to help their children avoid getting sick this flu season.

Preventing a Child from Getting the Flu

The most effective way to prevent a child from getting the flu is by administering a flu vaccination.

  • These vaccinations cause antibodies to develop within the patient’s body, protecting the individual against the influenza virus.
  • While a seasonal flu vaccination is not a 100 percent certain way to eliminate the flu, it has been shown to significantly improve the odds of a person avoiding a flu infection.
  • But a flu vaccination is not the only option parents have to fight the flu.

Parents can also incorporate better eating habits and hygiene into their children’s routines to help them persevere through flu season.

Where to Get a Flu Vaccination

Flu vaccines are available at many locations, particularly in health-related institutions, such as doctors’ offices, clinics, health departments, and pharmacies. Some schools will also facilitate a flu vaccination program to prevent a school-wide influenza outbreak. This broad level of availability means even children who do not have a regular doctor can get protection from influenza.

Facts About Flu Vaccinations

  • The CDC recommends that all children above six months of age (and most adults) receive the flu vaccine annually.
  • This vaccine is normally administered via a simple intravenous injection, but a nasal spray vaccination is currently being tested for widespread use.
  • The flu vaccine should take approximately two weeks to begin protecting against influenza.
  • If a person receives only one vaccination when he actually needs two, it may have no effect.
  • Vaccinations must be performed at least four weeks apart from each other.
  • Different flu vaccines are formulated to combat each strain of the flu virus.
  • Every year, medical researchers determine which flu virus will be most prevalent during the upcoming flu season and provide that information to flu vaccine manufacturers.

Use Proper Hygiene to Avoid Transmitting Influenza

The CDC advises that promoting proper hygiene is a fundamental way to stop the spread of germs that cause the flu. To this effect, parents should teach their children how to interact with their environment in a way that helps them avoid spreading or receiving the flu.

First, to avoid getting sick, children need to avoid close contact with people who already have the flu. Because the flu is spread by tiny droplets that are released from people’s mouths or noses, simply being near a flu carrier could allow an infection to take hold.

Conversely, people who know they have the flu should take extra precaution to minimize the impact of their infectiousness. Making the following simple changes to habits can also help prevent spreading the flu:

  • Eliminate germs by washing hands with soap and water or an alcohol-based solution when possible.
  • Limit contact with others as much as possible by staying home until symptoms subside.
  • Use a tissue or disposable cloth to cover the nose and mouth when coughing or sneezing.
  • Avoid touching hands to the eyes, nose, and mouth, as flu germs may be be on the hands.
  • Clean and disinfect any surfaces that may have been contaminated with germs.

Taking Antivirals to Treat Influenza

Antiviral drugs are prescription medications that fight viral infections. While the flu vaccine is highly effective for preventing the spread of influenza, it is not a guaranteed way of preventing the disease. When a person catches the flu, antiviral drugs may help the individual avoid a trip to the hospital. This medicine can potentially reduce the severity of symptoms and cut the length of the sickness by up to two days. There are currently two approved antiviral drugs for children that can be used this flu season:

  • Oseltamivir: Recommended by the CDC and American Academy of Pediatrics for treating influenza in children as young as two weeks old.
  • Zanamivir: Suggested medicine for treating children as young as seven years old.

This CDC guide to antivirals contains more information about who can take antiviral drugs and what impact they may have on one’s health.

During flu season, parents must keep track of their children’s health. If they can catch the signs of an influenza infection early, they can better comfort their children and take action to prevent them from spreading the flu to their peers and classmates. Furthermore, identifying a case of the flu early on has the added benefit of allowing parents to track a child’s condition as the disease progresses.

Parent Resources for Flu Season

Entering flu season while caring for a young child can be intimidating. Influenza causes upper respiratory problems that can lead to even worse health conditions if left unchecked. These resources will help parents get their families prepared for the upcoming flu season.

Advice for Diagnosing Influenza

There is a spectrum of tests that can be used to detect influenza. Some of them are faster and more accurate than others. Typically, patients will need to see a nurse or physician to receive a diagnostic test for the flu. For more information about how influenza is diagnosed, review the CDC’s guide for diagnosing the flu.

More Information About Vaccinations

The flu vaccine is widely available, but some people may be concerned about things such as when to receive a vaccination, why they actually need it, and whether getting vaccinated can have adverse effects. Learn more about the answers to these questions using the facts listed in this CDC guide to flu vaccinations.

More Information About Preventing the Spread of Influenza

The CDC also has guidelines for stopping the spread of germs that cause diseases, such as the flu, listed on its flu prevention steps page.

Common Influenza Complications for Children

When young children are infected with the flu, they usually experience the same symptoms as adults—typically fever, chills, muscle aches, nasal congestion, sore throats, and headaches. In addition to these symptoms, they are also prone to being afflicted by potentially severe health complications following contraction of the flu:

High Fever

A light fever in the range of 100-102 degrees F is a trademark symptom of influenza, but high fevers that exceed 104 degrees F may be more threatening to an individual’s health. This is especially true for children and the elderly. To identify whether a fever associated with the flu may require investigation by a medical professional, evaluate the following potentially dangerous high fever symptoms:

  • A temperature above 106.7 degrees F is extremely high and requires immediate medical attention.
  • A constant fever, especially one that persists for 14 or more days, may be the sign of a more dangerous infection.


Pneumonia is an inflammation of the tissue inside of a person’s lungs. In children, pneumonia commonly stems from the same virus as influenza. Therefore, pneumonia can be prevented by a collective effort to reduce the number of germs that are allowed to spread. This disease entails nearly the same symptoms as influenza but to a far more serious extent.

Additionally, people with pneumonia may experience confusion, muscle pain, and joint pain. These symptoms are generally more damaging to children and elderly people. Therefore, these groups have their health evaluated to determine whether their flu symptoms are improving or getting significantly worse.

Approximately 900,000 Americans get pneumonia each year, and between 5 and 7 percent die from it. Antiviral drugs can be used to limit the impact of the flu on the immune system, preventing severe symptoms and complications that may lead to pneumonia. For more about how to deal with pneumonia risks during flu season, visit the CDC page for preventing pneumonia.


Bronchitis is an infection of the main airways in the lungs. This condition can be caused by both viruses and bacteria, but viral bronchitis is more prevalent. In fact, bronchitis is most commonly caused by the same viruses as influenza and the common cold. Although minor bronchitis infection may cause only irritation or inflammation in these airways, a serious infection may last for up to three weeks (bronchitis caused by the flu is more likely to be severe). During the period, a person with bronchitis may experience the following symptoms:

  • Sore throat
  • Body aches and pains
  • A hacking cough
  • Fatigue
  • Nasal congestion

If a child experiences these symptoms alongside a constant fever (above 100.4 degrees F), it is likely that the child has caught a combination of bronchitis and the flu. If this occurs, parents should consider taking their children to be checked out by a physician. This is especially true if they have unusual symptoms:

  • A severe cough that lasts longer than three weeks
  • Coughing up mucus that contains blood
  • A high fever that lasts longer than three days
  • Chest pains or rapid breathing
  • Drowsiness and confusion

These symptoms are more serious, and the aid of a physician may be needed to rule out a potential lung infection, such as pneumonia. For more about how to deal with bronchitis risks during this flu season, visit the CDC page for preventing and treating bronchitis.

Middle Ear Infections

A middle ear infection is caused by germs that take up residence behind a person’s eardrum. This section of the ear is connected to the Eustachian tube, which is located behind the nose. Usually the body keeps the middle ear clean and dry by ventilating it through the Eustachian tube, but when this tube is blocked, the middle ear loses its outlet and becomes wet, stagnant, and warm.

Influenza can quickly trigger a middle ear infection by causing the Eustachian tubes to swell up, preventing airflow into the middle ear. Some harmful microbes may also climb through the Eustachian tube and get trapped in the middle ear, further stimulating the growth of an infection.

This is extremely important knowledge for parents, as young children and infants often have weak, immature Eustachian tubes that already have a difficult time staying open. When a child has the flu, their already weak Eustachian tubes are at far greater risk of succumbing to infection.

Repeated bouts with ear infections can lead to hearing loss or more serious infections. This makes it vitally important that parents help their children avoid the flu, thereby lowering their risk of ear infections. If a child with the flu is displaying any combination of the following symptoms, have the child’s ears examined by a health care professional as soon as possible:

  • Muffled hearing
  • Fluid draining from ear
  • Earaches
  • Irritability

For more about how to deal with ear infection risks during flu season, visit the CDC page for treating and preventing ear infections.

Flu Season Statistics Are Being Studied to Improve Population Health

Creating a historical record of the peak months of flu activity for each annual flu season is only one aspect of flu season statistics that are being studied. The CDC also operates a flu activity surveillance initiative that is called FluView. FluView is a weekly report that compiles flu activity data from medical institutions across the nation and processes that data into practical knowledge.

Some of the basic data presented in the FluView report shows approximately when and where influenza infections have been occurring frequently. The researchers also try to detect which strain of the virus is most prominent and whether that virus may be undergoing any changes or mutations. With this data on hand, the CDC can more effectively provide support to the groups of people who face the greatest risk of contracting a severe case of influenza.

Influenza reaches epidemic levels in the United States every year during flu season. Thankfully, organizations such as the CDC have compiled a large volume of evidence-based knowledge to help people safely persist through flu season. With these resources and modern medicine available, there is no reason to worry as flu season approaches this year.


What is H3N2v?
Some influenza A viruses occur naturally in pigs and can cause illness in those animals—these viruses are called “swine flu viruses”. While swine flu viruses do not normally infect humans, occasional human infections have occurred. When swine flu viruses infect humans, the viruses are called “variant viruses”.

The influenza A (H3N2) variant virus, or H3N2v, was first identified in pigs in the United States in 2010. In 2011, twelve cases of human infection with H3N2v occurred in five different states (not including Virginia). Since then, additional cases occurred, including one in 2013 in an out-of-state resident who had contact with swine in Virginia.

How can a person get H3N2v?
Influenza viruses can spread from people to pigs and from pigs to people. Spread from infected pigs to humans is thought to happen in the same way that seasonal influenza viruses spread between people – mainly through infected droplets created when an infected pig coughs or sneezes. If the droplets land in your nose or mouth, or you inhale them, you can be infected. Some evidence indicates that you might get infected by touching something that has virus on it and then touching your own mouth or nose.

How is H3N2v spread?
Most of the cases of H3N2v, including the one case with exposure in Virginia, had prolonged contact with pigs at agricultural fairs. Limited spread from person-to-person has also taken place; however, ongoing (sustained) transmission has not occurred.

What are the symptoms of H3N2v infection?
The symptoms of H3N2v infection are similar to the symptoms of seasonal influenza and can include fever and respiratory symptoms, such as cough and runny nose, and possibly other symptoms, such as body aches, nausea, vomiting, or diarrhea.

Is there a vaccine for H3N2v infection?
Currently, there is no vaccine for H3N2v infection. Scientists have taken early steps to start developing a vaccine; but, according to CDC, no decision to mass produce a vaccine has been made. The seasonal flu vaccine will not protect against H3N2v. Seasonal flu vaccines protect against seasonal influenza viruses. CDC recommends that everyone 6 months and older get a seasonal flu vaccine each year.

What is the treatment for H3N2v?
The same influenza antiviral drugs used to treat seasonal flu are used to treat H3N2v infection. The currently recommended drugs (oseltamivir and zanamivir) are available by prescription from your doctor. Early treatment works better and may be especially important for people with a high-risk condition. If you are prescribed antiviral drugs by your doctor, you should finish all of the medication, according to your doctor’s instructions.

How can I reduce the likelihood of getting H3N2v infection?

  • Some people are at higher risk for serious illness if they develop influenza, and should consider avoiding exposure to pigs and swine barns this fair season, especially if sick pigs have been identified. People at increased risk include children younger than 5 years old, people 65 years and older, pregnant women, and people with certain chronic medical conditions (like asthma, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions).
  • Wash your hands with soap and running water before and after exposure to pigs. If soap and water are not available, use an alcohol-based hand rub.
  • Never eat, drink, or put things in your mouth in pig areas, and don’t take food or drink into pig areas. Avoid close contact with animals that look or act ill.
  • Never take toys, pacifiers, spill-proof cups, baby bottles, strollers, or similar items into pig areas.
  • Cover your mouth and nose with a tissue or your sleeve (not your hands) when coughing or sneezing, and wash your hands often.
  • Avoid contact with pigs if you are experiencing flu-like symptoms. Avoid contact for 7 days after symptoms begin or until you have been fever-free for 24 hours without the use of fever-reducing medications, whichever is longer.
  • If you must be near pigs that are known or suspected to be infected with influenza viruses, wear gloves and a mask to cover your mouth and nose.
  • If you develop a flu-like illness after exposure to pigs, see your doctor. Tell the doctor that you have had recent exposure to pigs.

For more information on H3N2v:

  • CDC
    • H3N2v and You
    • Key Facts for People Exhibiting at Fairs
    • Protect Yourself Against H3N2v (fact sheet)
  • United States Department of Health & Human Services – H3N2v
  • Virginia Department of Health (VDH)
    • Novel and Variant Influenza Viruses: Information for Healthcare Professionals
    • Influenza fact sheet

FRIDAY, Feb. 22, 2019 (HealthDay News) — Americans aren’t out of the woods yet, as the flu season continues to spread across the country, health officials reported Friday.

One major shift that’s occurred is in the viruses that are circulating. At the start of the flu season, the predominant strain was influenza A H1N1, but now a more severe strain, influenza A H3N2, accounts for nearly half of all the new cases, according to the U.S. Centers for Disease Control and Prevention.

“It looks like we are moving from an H1 wave to an H3 wave,” said Lynnette Brammer, lead of CDC’s domestic influenza surveillance team. “There’s still a lot of flu to come.”

On the plus side, this year’s vaccine is more effective than last year’s was. According to Brammer, this vaccine is 62 percent effective against H1N1 and 44 percent effective against H3N2.

For children aged 6 months to 17 years, overall vaccine effectiveness is 61 percent, according to the CDC.

Getting kids vaccinated is crucial. This season, flu has already claimed the lives of 41 children.

Behind that statistic lie very real tragedies and heartbreak:

  • In Lowell, Mass., CBS News reported that 4-year-old Puthiraksmey Paak passed away Feb. 16 due to complications from flu. Her heartbroken father, Sopheak Paak, said his family had recently moved to the United States from Cambodia in search of a better life.
  • In San Diego, NBC News reported the first child death this season from flu in that city occurred when Julie Leyva Campos, 14, succumbed to the illness Feb. 12. Family members said she hadn’t gotten a flu shot and had an unspecified underlying medical condition.
  • And on Feb. 18, an 8-year-old boy, Martin Ray “Chucky” Campbell Jr., of Rockport, Texas, died only hours after being diagnosed with flu, NBC News reported. “He had a lot to say and now it’s just quiet,” Campbell’s aunt, Jessica Solis, told NBC.

So, Brammer is still urging people who haven’t been vaccinated to get their shot. “As long as flu is circulating and you haven’t been vaccinated, we recommend that you go ahead and get vaccinated,” she said.

‘Aussie flu’: A/H3N2 strain of influenza behind worst WA flu season in almost a decade

It was dubbed the “Aussie flu”, and now the influenza strain that wreaked havoc in the northern hemisphere and Eastern States two years ago has hit WA, triggering a rapid rise in serious flu cases.

The dominant influenza A virus A/H3N2 caused the worst flu season Australia had experienced in almost a decade.

Camera Icon Flu claimed the life of Perth 10-year-old, Faithfull, last weekend. Credit: Supplied

When it hit Britain last year, the local press labelled it the “Aussie flu”, despite the fact that its origin was not proved to be Australia.

At the time experts predicted the deadly virus, which had mutated from the strain given in the flu vaccine at the time, would hit WA just as badly, but the State was fortunate and managed to remain relatively unscathed. Until now.

This year, 11 people have died in WA from flu-related illness, including 10-year-old asthmatic boy Mataiapo Faithfull Puttz William Maku this week, compared with four at the same time last year. In the Health Department’s latest Virus Watch report, 75 per cent (or 169) of the 229 WA samples that tested positive for flu at PathWest were the A/H3N2 strain.

It has been a horror and early start to the flu season, with a spike in flu cases coming two months earlier than usual.

Despite the results, Health Department acting director of communicable disease control Paul Effler said there was “no information to indicate that the A/H3N2 influenza virus circulating in WA was more virulent than previous A/H3N2 viruses from previous seasons”.

Australian Medical Association WA president Omar Khorshid said A/H3N2 had not been the dominant strain in WA since 2016. “That was the last big epidemic I guess you’d say of A/H3N2 here and it was the biggest peak epidemic as far back as 2012,” he said.

Because A/H3N2 has not been dominant in Perth for three years, West Aussies have less immunity to it.

Camera Icon Daily Star front page January 11, 2018. Credit: Daily StarCamera Icon Daily Star front page December 15, 2017. Credit: Daily Star

“That’s why it’s having an effect now,” Dr Khorshid said.

“But if people have had their flu vaccine, they will be immune to this strain.

“There’s nothing about this flu apart from its timing that should scare people in WA.”

He stressed that while A/H3N2 was hard on the elderly, “all flus are dangerous to the elderly, kids and people with impaired immunity”.

The department’s latest weekly Statewide notifiable diseases data shows that the number of reported flu cases in WA this year has risen by 874 in one week to 3887.

Camera Icon Josh Johnston, 9, recovering from the flu in Perth Children’s Hospital with mum Rachel. Credit: Justin Benson-Cooper

The flu vaccine is designed around four specific strains each year, based on which viruses dominated in the northern hemisphere the previous winter. “Sometimes they get it wrong but this year’s vaccine has the A/H3N2 strain,” Dr Khorshid said.

What we know about the A/H3N2 strain

While all influenza viruses are always mutating, A/H3N2 evolves more rapidly than A/H1NA and influenza B, meaning the vaccine can become ineffective once the strain mutates.

Flu symptoms

In adults, typical symptoms include sudden fever, head-ache, sore throat, cough, fatigue, general aches and pains, and nose, throat and lung congestion.

Flu symptoms in children can include additional symptoms such as nausea, vomiting and diarrhoea.

The flu lasts longer than a cold, is highly contagious and does not cause a runny or stuffy nose.

What to do if you have it

If you have mild symptoms and are not at increased risk of developing severe illness from the flu, stay at home and rest.

Eat healthily, drink a lot of fluids and take paracetamol to help reduce fever and aches.

Make sure to wash your hands often, cover your mouth when coughing or sneezing and immediately throw away used tissues.

If you are at higher risk of developing a serious illness or health complications from the flu (children, pregnant women, the elderly and people with chronic medical conditions), see a doctor.

Go to your doctor if you have breathing problems, your skin starts to turn blue, you have pain or pressure in your chest or abdomen, you experience dizziness or confusion, you have a rash or you are vomiting persistently.

GP Sean Stevens from Currambine Family Practice said if people had symptoms but were not sure it was flu, they should see a GP.

How long to stay home from work

Dr Stevens said it was vital to stay home “until you feel recovered”. “It could take anywhere between five and 12 days,” he said.

How to prevent the flu

The best way to prevent catching the flu is to have the vaccination, according to the Health Department.

Try to avoid people with the flu, wash your hands, cover your mouth with a tissue while coughing and sneezing. If you don’t have a tissue, cough or sneeze into your elbow.

What are Influenza Type A Flu and Type B Flu?

When it comes to the flu, not all types are created equal. You’ve probably heard that there are a few different types of the flu. According to the CDC, there are three types of influenza viruses: influenza A, influenza B and influenza C. Influenza A and B are the two main types that routinely spread in humans and cause seasonal flu epidemics. Influenza C viruses cause only mild respiratory infections and are not thought to be responsible for epidemics. 14, 15

Influenza A vs B: Brief History & Transmission

Influenza A viruses are the most harmful, as they can cause severe disease. Wild aquatic birds are often the hosts for a large variety of influenza A viruses. Sometimes these viruses are transmitted from bird to human and can cause devastating outbreaks. Some of the subtypes of influenza A that have caused the largest number of known human deaths are:14, 15

  • H1N1, which caused Spanish Flu in 1918 and Swine Flu in 20091

  • H2N2, which caused Asian Flu in 19572

  • H3N2, which caused Hong Kong Flu in 19683

  • H5N1, which caused Bird Flu in 20044

Influenza B almost exclusively infects humans and is less common than influenza A. Flu type B also mutates about two to three times more slowly than influenza A. Because humans are the natural host of influenza B, pandemics generally do not occur with influenza B viruses.22 Although scientists can classify and monitor the different types of flu viruses, it is virtually impossible for them to develop effective vaccines that provide lifelong immunity. The reason: Flu viruses mutate (change their genetic structure) and replicate (produce new, identical copies of themselves) extremely quickly, making it difficult for scientists to keep up.22

Signs of Influenza A or Influenza B Symptoms

The good news is most people will recover from the flu on their own. However, if you have a severe case of the flu, you should see your healthcare provider. Not sure if you have the flu? A good indication of whether or not you have the flu is if a thermometer indicates you have a fever.

Influenza A and Influenza B Treatment

While over-the-counter medications cannot cure the flu, they can help ease your symptoms while you wait for it to run its course. If you’re suffering from a sore throat, headache, cough, fever, runny nose, or minor aches and pains, NyQuil Cold & Flu and DayQuil Cold & Flu are both good options since they contain a pain reliever/fever reducer and cough suppressant. If you’re suffering from more symptoms, try NyQuil SEVERE Cold & Flu, which also contains a decongestant, and DayQuil SEVERE Cold & Flu, which has an expectorant to help loosen congestion in your chest. Soon enough, you’ll be on the road to recovery.

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Flu Season Is Still Going, A New More Severe Strain Now Circulating

If you don’t take the proper precautions, this may be you. (Photo: Getty Images)


Taylor Swift once sang, “Are we out of the woods yet? Are we out of the woods? Are we in the clear yet?” She probably wasn’t singing about this year’s flu season. But if she had been, the answer would be “No, no, and no.” The flu season is not over. In fact, there’s now a new potentially nastier strain of the flu virus making the rounds.

If you look at the latest flu activity map on Fluview, the Centers for Disease Control and Prevention’s (CDC’s) Weekly U.S. Influenza Surveillance Report, you will see lots of brown. In fact, every state and territory is brown except for Texas, Tennessee, Washington, DC, Vermont, and the U.S. Virgin Islands. On this map, what can brown do for you? It can show you where flu activity is still considered “widespread” in the tenth week of 2019, which ended on March 9, 2019. In fact, as of that week, 30 states still had high influenza-like illness (ILI) activity. Only four states (Arizona, Delaware, Florida and Tennesse) had minimal ILI activity.

Why is it ILI activity and not flu activity? The CDC can track ILI activity and not actual flu activity because not everyone who has flu-like symptoms actually gets tested for the flu. There are other pathogens like adenovirus, the respiratory syncytial virus (RSV), or the parainfluenza virus that can cause symptoms that mimic the flu.

You may think, “hey, isn’t it mid-March? Shouldn’t we be out of the woods yet?” Nuh-uh. Take a look at data from the Centers for Disease Control and Prevention (CDC), which shows which month flu activity peaked in the United States over the past 36 flu seasons from the 1982-1983 flu season through the 2017-2018 flu season. The most common month was February (containing the peak in 15 seasons). Second place was December (7 seasons), followed by January (6 seasons) and then March (6 seasons). It’s a myth that flu is exclusively a cold weather virus. You can still get the flu when it is warm outside.

Moreover, the peak certainly doesn’t mean the end of flu season. In fact, the peak typically represents the middle of the flu season. If we have just gotten past the peak, expect the flu season to drag on for at least another month or so.

Unfortunately, people are still dying from the flu. In week nine of 2019, pneumonia and influenza accounted for 7.2% of all the deaths that occurred. In the tenth week of 2019, the CDC received reports of four more kids dying from the flu, bringing to 68 the total number of kids who died because of the flu in the 2018-2019 flu season.

H1N1 may have been the dominant influenza strain early on, but lately another seemingly nastier strain, H3N2, has gained momentum, according to the Centers for Disease Control and Prevention’s latest report. Throughout the season, the H1N1 has constituted the majority (67.2%) of samples taken since September 30, 2018. However, in the tenth week of 2019, H3N2 was in 61.3% of the samples. This second strain could stretch out the flu season longer. Plus, reports are that this year the H3N2 strain is getting people more sick than the milder H1N1 strain.


Therefore, if you haven’t gotten the flu vaccine yet, it is still not too late to get it. That’s because we are still not out of the woods yet, we’re still not out of the woods, we are still not in the clear, yet. You can still get the flu. The flu vaccine seems to more effective this year than last year. A Centers for Disease Control and Prevention (CDC) report estimated that the vaccine has been 47% effective at preventing acute respiratory illnesses caused by all influenza virus types. That would mean that if you get the flu vaccine, on average, your chances of getting the flu, complete with the typical symptoms, would drop by about 47%. Getting the flu ranks somewhere below repeatedly hitting yourself with a chair in terms of things that you want to do. The flu is not just a cold or some other more minor illness. The flu can really wipe you out and even kill you, no matter how healthy you think you are.

The basis of the vaccine effectiveness estimate was measurements from a sample of 3,254 children and adults who were part of the U.S. Influenza Vaccine Effectiveness Network, from November 23, 2018 to February 2, 2019. Researchers estimated the effectiveness of the flu vaccine by comparing the rates of flu among those who got the vaccine versus those who did not get the vaccine. Those who got the vaccine were, not surprisingly, less likely to have gotten the flu. The vaccine effectiveness was 61% among children who were 6 months to 17 years old and 24% among those 50 years and older.

Estimates by the CDC from mid-November 2018 suggested that vaccination rates have increased this year, compared to last year. Last year, a relatively low 37.1% of the population got vaccinated, according to a CDC report. That was 6.2% less than the percentage who got vaccinated the previous flu season. The flu ended up killing nearly 80,o00 people last year. The November 2018 estimates showed that 45.6% of kids (6 months to 17 years old) had gotten the flu vaccine, which was 6.8% higher than estimates from November 2017. The November 2018 estimated also showed vaccination rates to be 44.9% among adults, which was a 6.4% increase from the previous year.

So, yes, we’re not out of the woods yet. You should still get the vaccine if you haven’t yet already. And whether Pete Hegseth was actually joking about this or not, don’t believe that you can somehow “inoculate” yourself. Wash your filthy hands frequently and thoroughly.

H3N2v and You

What is H3N2v?

H3N2v is a non-human influenza virus that normally circulates in pigs and that has infected humans. Viruses that normally circulate in pigs are “swine influenza viruses.” When these viruses infect humans, they are termed “variant” viruses.

In 2011, a specific H3N2 virus was detected with genes from avian, swine and human viruses and the 2009 H1N1 pandemic virus M gene. The virus was circulating in pigs in 2010 and was first detected in people in 2011. The acquisition of the 2009 M gene may make this virus infect humans more easily than is typical for other swine influenza viruses. The most up to date information about H3N2v cases, hospitalizations and deaths that have been reported to CDC is available at: Case Count: Detected U.S. Human Infections with H3N2v by State since August 2011.

How can a person catch a flu virus from a pig?

Influenza viruses can spread from pigs to people and from people to pigs. Spread from infected pigs to humans is thought to happen in the same way that seasonal influenza viruses spread between people; mainly through infected droplets created when an infected pig coughs or sneezes. If these droplets land in your nose or mouth, or you inhale them, you can be infected. There also is some evidence that you might get infected by touching something that has virus on it and then touching your own mouth or nose. A third possible way to get infected is to inhale particles containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common.

What are the symptoms of H3N2v?

Symptoms of H3N2v infection are similar to those of seasonal flu viruses and can include fever and respiratory symptoms, such as cough and runny nose, and possibly other symptoms, such as body aches, nausea, vomiting, or diarrhea.

Why is CDC concerned about H3N2v?

CDC is concerned about H3N2v for a few reasons.

First, infections with influenza viruses (including variant viruses like H3N2v) can sometimes cause severe disease, even in healthy people. This can include complications (like pneumonia), which can require hospitalization, and sometimes result in death.

Second, this virus seems to spread more easily to humans from pigs than other swine influenza viruses.

Third, influenza viruses are always changing. It’s possible the H3N2v virus could change and begin spreading easily from person to person.

Fourth, studies conducted by CDC and others have indicated that children born after 2001 (age ≤9 years at 2010) have little to no immunity against H3N2v viruses. Adults seem to have more immunity, perhaps because they might have been previously exposed to similar viruses in their lifetimes.

Is H3N2v dangerous?

Currently, the severity of human illness associated with H3N2v resembles that of seasonal flu.

Keep in mind that even seasonal influenza can be a serious disease. Sometimes seasonal influenza can lead to complications (like pneumonia). It also can lead to hospitalization and even death.

Is there a vaccine for H3N2v?

Early steps to make a vaccine against H3N2v have been taken. A pilot H3N2v vaccine was produced and preliminary clinical studies indicated that it leads to a significant immune response.

Will this season’s flu vaccine protect me against H3N2v?

Seasonal flu vaccine will not protect against H3N2v. Seasonal flu vaccines protect against seasonal influenza viruses. CDC recommends that everyone 6 months and older get a seasonal flu vaccine each year.

Is there treatment for H3N2v?

Yes. The same influenza antiviral drugs used to treat seasonal flu can treat H3N2v in children and adults. The currently recommended drugs – oseltamivir, zanamivir, peramivir, and baloxavir – are available by prescription from your doctor.

Early treatment works best and is especially important for people with a high risk condition.

If you are prescribed antiviral drugs by your doctor, you should finish all of the medication, according to your doctor’s instructions.

Who is at high risk of serious H3N2v illness?

People who are at high risk of developing complications if they get seasonal flu include the following: children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions).

A full list of people at high risk of flu related complications is available at People at High Risk of Developing Flu-Related Complications. These same groups of people are thought to be at high risk of developing serious complications from H3N2v infection.

CDC has issued guidance for people attending fairs where swine might be present this fair season, including additional precautions for people who are at high risk for serious flu complications.

Can I get H3N2v from eating pork?

No. Influenza viruses have not been shown to be transmissible to people through eating pork (pig meat).

How many people have been infected with H3N2v?

See Case Count: Detected U.S. Human Infections with H3N2v by State since August 2011 for the most up to date information about H3N2v cases, hospitalizations and deaths reported to CDC.

Who has been infected by H3N2v?

Most H3N2v infections have occurred in children with exposure to swine; many have occurred at agricultural fairs.

What is CDC doing about this situation?

CDC continues to communicate regularly with states, and states have continued with surveillance and laboratory activities to detect human cases of H3N2v.

CDC also continues to monitor the situation closely. In particular, CDC’s Influenza Division examines the genes of many of the H3N2v viruses that are shipped by state public health laboratories to CDC to ensure that the virus is not changing in key ways.

What should I do if I am at an agricultural fair?

See Take Action to Prevent the Spread of Flu Between People and Pigs at Fairs for a list of steps you can take to protect yourself against H3N2v.

In particular, if you are at high risk of serious flu complications, avoid pigs and swine barns at the fair.

Should I avoid agricultural fairs where swine are present?

It’s not necessary to avoid agricultural fairs where swine are present. However, you should take steps to protect yourself against H3N2v if you do attend agricultural fairs, particularly where swine are present.

If you are at high risk of serious flu complications, avoid pigs and swine barns at the fair.

Should people avoid pigs and swine barns?

People with health or age factors that put them at high risk for serious flu complications should avoid pigs and swine barns.

Are there things I should do, even if I’m not around pigs?

As always, take time to get a seasonal influenza vaccine as soon as flu vaccine becomes available in your community, to protect yourself from the seasonal influenza viruses that are most likely to circulate this season.

Can you tell if a pig has the flu?

No, you cannot always tell if a pig has a flu virus just by looking at the pig. Some pigs infected with influenza may have no signs of illness at all. See Key Facts About Swine Influenza (Swine Flu) in Pigs for a list of signs of flu in pigs.

Is H3N2v the same as the H3N2 flu virus that makes people sick each flu season?

No, H3N2v is different. H3N2v is a variant virus that is in pigs and has infected some humans.

Photo: H. Armstrong Roberts/ClassicStock/Getty Images

Last year, an estimated 80,000 people in the U.S. died from flu-related complications, according to data from the Centers for Disease Control and Prevention, making the last flu season the deadliest in at least four decades. With that in mind, it’d be understandable if you’re worried about this year’s flu: wondering whether it will be as severe as last season’s and what you can do to prevent the virus from affecting you. Here’s the latest news from the CDC on the 2018 – 2019 flu season, and some insight from flu experts.

First things first, do we know if this year’s flu season will be as bad as last year’s?
The CDC started monitoring the flu in October, and the season should last through the spring. Earlier this month, Kristen Nordlund, press officer for the CDC, told the Cut, “It is too early to say how severe the season will be, however, flu activity is expected to continue to increase over the coming weeks.” But even though it’s early, we have some information about what’s going on with the flu.

So, what is going on with the flu right now?
The CDC’s latest weekly flu surveillance report accounts for flu instances through January 12. The CDC estimates that, since monitoring began on October 1, over 8 million Americans have had the flu. More than 4 million people have gone to the doctor with flu symptoms so far, and between 95,000 and 114,000 people have been hospitalized. Nineteen children have died from the flu so far this season.

Are we going to get data like this each week?
Yes. The CDC has released weekly surveillance reports in previous flu seasons — but it hasn’t released weekly estimates like this in the past. “This is the first year that we’re actually reporting these numbers during the season, and going forward we’re going to be reporting them every week,” Dr. Alicia Fry of the CDC told NBC News. So, we’ll keep updating this post as new data becomes available.

Okay. But how does the flu this year compare to last year’s?
Flu expert Stephen Ferrara, associate dean of clinical affairs at Columbia University School of Nursing, told the Cut that as of earlier this month, the flu season has been following a more traditional pattern — in contrast with last year’s, which was more unpredictable. So there are already some visible differences. However, although it looks like this year’s influenza may not be severe as last year’s, Ferrara stressed that the flu is always dangerous in any circumstances.

Wait, please explain these “differences.”
Basically, each year, different mutations of the influenza virus circulate; certain strains tend to be more dominant than others, depending on the season. The prominent strain last year was Influenza A (H3N2). The virus circulated earlier in the season than usual and was more virulent than had been seen in prior years, which contributed to it being a particularly difficult strain, according to the expert. On top of that, after the H3N2 virus reached its peak by early February, a strong surge of Influenza B cases popped up and spread through the spring. That’s a fairly regular occurrence after a H3N2 spread, but different than what you might see after other strains reach their peaks.

So this year, Ferrara notes the flu seems to be following a more “predictable” pattern: There’s been the traditional spike in cases in the weeks of December, and a more common strain — Influenza A (H1N1) — has so far been dominant. There are still cases of H3N2, but fewer than last year. But keep in mind that both of these strains are still mutations of the same Influenza A virus; it’s just that we’re more likely to have built up some immunity to H1N1 (which emerged in 2009), whereas H3N2 is a newer mutation.

Excuse me … are you talking about the swine flu?
Yes, H1N1 is also known as the “swine flu,” but please don’t be overly alarmed. The strain is dangerous — say it with me: All strains of the flu are dangerous — but this outbreak should not be as bad as the 2009 pandemic, which one study found may have led to approximately 280,000 deaths worldwide. You see, during the pandemic, a special vaccine for the H1N1 strain was created — and the strain also became a more regular fixture of flu seasons moving forward. So, our bodies (hopefully) now have some immunity to it. Ferrera told the Cut that now, a typical flu vaccine includes two variants of Influenza A (both H1N1 and H3N2) and at least one strain of Influenza B, so if you get the flu shot, you will hopefully be covered.

So, you’re saying I should get a flu shot?
Please forgive this emphasis, but yes, yes, yes, a million times yes! According the CDC’s Nordlund, the flu vaccine is the safest bet to reduce the risk of the flu and its serious complications. I got my flu shot back in October, but Ferrara says it’s not too late for others to do the same. “We continue advocating for people to get them, and especially now, if people were to get it, it will cover them in the typical peak season,” he said. “It does take your body about 10 to 14 days to develop immunity from the vaccine, but certainly there is still time. We haven’t seen the worst of this season yet.”

Other than that, how can I prevent the flu?
It’s still the same common-sense practices we were taught as children: Wash your hands and/or use alcohol-based sanitizer, stay home when you’re sick, cover your mouth if you cough, dispose of dirty tissues in a way that won’t make other people exposed to them, and avoid being around sick people if you can.

What flu symptoms should I keep an eye out for in the 2018–2019 season, and what should I do if I think I’m coming down with the flu?
Ferrara told the Cut that there are some very classic flu symptoms to keep an eye out for: a nonproductive cough, fever, and body/muscle aches in adults; and children may also experience nausea and vomiting on top of those other symptoms. So, if you’re experiencing any of that, it’s important to head to the doctor immediately. There’s an antiviral drug that can be taken within the first 48 hours of the flu that might help you (if your doctor decides you’re a good candidate for the medication). Nordlund noted that people at risk of serious complications from the flu and children should especially seek immediate medical assistance.

And how long does the flu last?
Generally speaking, when it comes to the flu, acute illness can last four or five days, though your cough can linger for weeks. But it can also take a while to snap back from the flu, since “it really is debilitating, especially if you have a full-blown case,” Dr. Arnold Monto, a professor of epidemiology at the University of Michigan School of Public Health, told the Cut last year. People are usually only contagious for five days at the most if they have the flu (and maybe a bit longer if they’re younger), and it’s recommended that people stay home from work three to five days if they’re sick.

This post has been updated.

What You Need to Know About the 2019–2020 Flu Season

But the dominant strain of flu there this season, H3N2, usually leads to more serious symptoms and hospitalization compared with the common H1N1 strain. Last year’s U.S. flu season saw the dominant strain flip from H1N1 to H3N2 around March 2019.

During the winter of 2017–2018, when H3N2 prevailed, the CDC reported that more than 80,000 people died of influenza in the United States, making it one of the deadliest flu seasons in decades.

“It looks like H3N2 may be the dominant virus this year in the United States, and that tends to cause more severe illness,” says Schaffner.

No Matter the Strain, Flu Is Serious

The CDC warns that any type of flu can be far worse than the common cold. The illness can come on quickly and produce fever, cough, sore throat, runny or stuffy nose, body aches, headaches, and fatigue.

A bad case of flu can bring on vomiting and diarrhea. Some people develop complications, ranging from mild sinus and ear infections to potentially fatal pneumonia and inflammation of the heart, brain, and muscle tissues.

“The flu is a contagious and serious respiratory illness that can result in serious complications, and death,” says Dr. Taege. “Every year thousands of people, including children, die from the flu. Young children, older adults, pregnant women, and people with certain chronic conditions are the most vulnerable to complications.”

Your Best ‘Shot’ at Protection

The CDC advises that everyone age 6 months and older get a flu vaccine every season. The vaccine — now administered through an injection or nasal spray — is widely available in physician offices, clinics, some workplaces, and pharmacies all over the country.

The vaccine can reduce related sicknesses, doctor’s visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations and death.

A 2017 CDC study showed that vaccination can significantly lower a child’s risk of dying from the illness.

The CDC also endorses the vaccine as safe and effective for pregnant women. Some of the protection gained by the mother crosses the placenta and gets passed on to the newborn during the first six months of the baby’s life, before he or she is eligible for vaccination.

“It’s not a perfect vaccine, but it still does a lot of good,” says Schaffner. “Even if you get flu after having had the vaccine, you’re likely to have a less severe infection. You’re less likely to get complications of pneumonia and go to the hospital. That’s been shown year in and year out.”

Taege adds that vaccination helps suppress the dreaded spread of the disease.

“By getting vaccinated, you are not only protecting yourself, but you’re protecting those around you by lessening the amount of flu in the community,” he says.

Despite reports that tens of millions of vaccines may ship late this season, Schaffner does not anticipate that the delays will significantly affect opportunities for immunization.

“If you haven’t been vaccinated by Thanksgiving, run, do not walk, because most of the time flu peaks in the United States in February,” he says. “We can’t predict the severity of the upcoming flu season, but we can predict that there will be flu. So get vaccinated.”

Enlarge/ A child received a vaccination against influenza A (H1N1).

The 2019-2020 flu season is up and running—and so far, it’s off to a weird start.

Flu activity has been elevated since the start of November and is only expected to continue climbing, the Centers for Disease Control and Prevention reports in its latest flu update. That’s a few weeks earlier than in past years.

Flu season in the United States can ramp up in the fall and peak anywhere between December and March, then drag itself out as late as May. In the last 36 years, flu most often ramped up in December and January and peaked in February. But for this winter, the CDC says there’s a 40 percent chance the flu will peak in December based on activity so far.

  • Influenza-like illness reports for this flu season (red) and past seasons. CDC
  • During this 36-year period, flu activity most often peaked in February (15 seasons), followed by December (7 seasons), January (6 seasons) and March (6 seasons). CDC

While this season may peak on the early side, the most unusual aspect is that it’s being driven by an influenza B strain. This isn’t necessarily good or bad, just unusual.

Type B is one of three types of influenza viruses that infect humans—A, B, and the very mild C. (There’s a fourth type, D, but so far it mainly seems to infect cattle.) Most flu seasons are driven by type A viruses, the kind you’ve probably heard about the most. Type A viruses are identified by numbered Hs and Ns, like H1N1 and H3N2.

Viral code

The Hs and Ns refer to hemagglutinin (Ha or H) and neuraminidase (Na or N), respectively, which are both viral molecules that hang on the outside of viral particles. Basically, Ha helps viral particles invade human cells in the respiratory tract and Na allows newly formed viruses to burst out of human cells and invade more (for more details, see this explainer). But, because they jut out from a viral particle, Ha and Na also help our immune systems identify flu virus. This essentially triggers an arms race.

Type A viruses can swiftly mutate and rearrange the molecular makeup of Has and Nas, making them difficult if not impossible for our immune systems to recognize. That’s where the numbering comes in. There are 18 Ha subtypes and 11 Na subtypes known, creating 198 possible combinations. To make things more interesting, type A viruses are promiscuous—they infect humans, many mammals, and birds. This gives them a lot of opportunities to swap their Has and Nas and come up with exciting combinations. Occasionally, extremely dangerous combinations can spark pandemics, such as the deadly H1N1 “swine flu” that spread worldwide in the 2009-2010 flu season. The ever-morphing nature of type A viruses is the main reason why flu can be so deadly and why we need to get different flu shots every season.

Type B viruses—which are dominating this flu season so far—don’t do any of this. Their Has and Nas genetically “drift” relatively slowly. Type B viruses also only infect humans and, oddly enough, seals, giving them fewer opportunities to mingle and rearrange themselves. Since type B viruses were first spotted in the 1940s, they have never been linked to a pandemic.

Instead of a soup of numbers, Hs, and Ns, type B viruses are mainly identified by their lineage. In the 1980s, geneticists noted that type B viruses seemed to have split into two distinct, evolutionary lineages based on studying their Has. They dubbed the lineages B/Victoria for a reference stain isolated in Australia and B/Yamagata after a reference strain isolated in Japan.

Type B viruses typically account for about a third of all of the flu disease burden. For many years, researchers had the impression that they were relatively mild flu strains, given their slow evolution and limited host-hopping. But recent studies have found that they can cause severe disease and sometimes cause the bulk of flu-related deaths in a season. Type B viruses are also detected most often in children.

Latest data

According to the latest surveillance data from US surveillance programs, around 60 to 70 percent of the flu viruses analyzed from patients this flu season have been type B viruses. Of those, about 97 percent tested were in the B/Victoria lineage. Over the last few weeks, the proportion of B/Victoria strains among the flu-positive cases has been increasing.

It’s unclear why B/Victoria is surging or what that surge means for the rest of the flu season. CDC spokesperson Scott Pauley told Ars over email that flu is difficult to predict and that it’s simply “too early to make any kind of assessment about the potential severity of the season.”

  • Influenza-positive tests reported to the CDC. The green sections of the bars represent type B viruses. CDC
  • Influenza-positive tests from public health labs by week. The data is shown in the span of the typical flu season. CDC
  • Influenza-positive tests from clinical labs. CDC
  • Flu-activity by state. CDC

We should also note that cases of type B viruses have been relatively low in recent years and almost non-existent in the 2018-2019 flu season. This may mean that there’s less immunity in the population overall.

Some good news is that early testing suggests that most of those B/Victoria strains now roaring back are B/Colorado/06/2017-like (Victoria lineage), which are covered by this year’s flu vaccine.

Otherwise, very small samplings of the type A viruses popping up this season—H1N1 and H3N2 viruses—suggest that they’re nearly all similar to the A/Brisbane/02/2018 (H1N1)pdm09–like virus and the A/Kansas/14/2017 (H3N2)–like virus, which are both covered by this year’s flu vaccine.

Get vaccinated

However, as CDC’s Pauley noted to Ars, “there is relatively little laboratory data on the characterization of viruses collected since October, so it’s not possible to make conclusions about how well the vaccine will work at this time.”

There has been some concern that the flu vaccine recommended for the 2020 flu season in the Southern Hemisphere includes different H3N2 and B/Victoria lineage viruses than the 2019-2020 vaccine for the Northern Hemisphere. But again, flu seasons are notoriously difficult to predict, and it’s still too early to say what will happen.

Regardless of how well-matched this year’s vaccine will be to circulating flu viruses, getting a flu shot is critical, Pauley notes to Ars. The vaccine can spare you entirely and prevent disease spread or, at least, dampen the severity of the infection, potentially saving lives. “Flu vaccination is the best way to reduce the risk from flu and its potentially serious complications,” Pauley says.

So far in the US, there have been six confirmed pediatric deaths from flu this season. Overall, the CDC estimates that there have already been at least 1.7 million flu cases nationwide this season, leading to at least 16,000 hospitalizations and 910 deaths. Southern states have been hardest hit.

This year the flu came in two waves—here’s why

Graphical representation of an influenza virus illustrating the proteins exposed on the surface. Credit: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases, CC BY

The just-ended 2018-2019 flu season was relatively mild compared to the last season, during which nearly 80,000 people in the U.S. died of flu-related illness, according to estimates by the U.S. Centers for Disease Control and Prevention.

This year’s death toll is predicted to be about half, or, in the worst case, three-quarters of that number.

The 2018-2019 season has been unusual, though, because the flu came in two waves: one that peaked at the end of December, and a second that peaked in early March. The two peaks were caused by two different strains of the flu virus, and the protection given by vaccination early in the season may have waned by the time the second strain appeared.

Flu epidemics reoccur every year because of the way the virus is built and how it interacts with the human immune system. The viruses are highly changeable, acquiring genetic variations, called mutations, even within a single season. The new properties conferred by these mutations can allow the virus to evade the immune response elicited by the flu vaccine.

In addition, the immunity conveyed by a flu shot does not last from year to year. In fact, depending on the flu strain that is circulating, immunity may not even last through one flu season.

Here’s how it all added up over the flu season that has just drawn to a close.

Having flu once can protect from the same virus

When you’re first exposed to the live flu virus, your immune system shifts into gear to try to fend off the invader. Specialized white blood cells, called B-cells, make antibodies that attack two proteins that poke off the surface of the virus, preventing them from doing their jobs. These viral surface proteins, called haemagglutinin (HA) and neuraminidase (NA), are necessary for the virus to survive.

Your immune response may not be fast enough to stop the virus from successfully invading your respiratory tract cells and causing flu symptoms. However, over the course of the infection different parts of the virus evoke an immune response that is more extensive and longer lasting.

Once the infection is over, special cells, called memory B-cells, lie dormant, waiting for a second invasion of the same virus. If they recognize the previously fought flu virus, they launch a rapid immune response.

Vaccines are designed to get your immune system ready to confront a virus without having to first be infected to learn about it. Every year, the World Health Organization predicts which flu strains will circulate and vaccines are formulated with the anticipated strains.

Credit: The Conversation

Almost all current flu vaccines are made with killed virus. After injection, most of the antibodies made by the immune system’s B-cells are directed toward the “head” region of HA, the part that’s sticking furthest off the protein stalk from the surface of the virus. These antibodies prevent subsequent infection because the HA head is what makes first contact with the cells of the respiratory tract.

Because the dead viruses in the vaccine do not infect and grow, the wave of antibodies they induce is fairly short-lived and the vaccine is not great at creating memory cells. The challenge to your immune system from the vaccine is much more limited than if it were facing a full-on onslaught of live viruses.

That short memory is one reason why you need to be vaccinated every season—even if the same virus is circulating, your immunity to it may be gone by the next year.

Flu virus can change to outflank immune system

The immune systems of all the people exposed to the flu virus are constantly attacking HA and, to a lesser degree, NA. This means that substrains of the flu virus with small changes in these proteins that allow them to evade the attack are more likely to survive—and so get passed on and become more common. This progression of small changes in the virus is called antigenic drift.

Flu viruses also can change more drastically by picking up genetic material from flu viruses in other animals, such as birds and pigs, a process called antigenic shift.

Antigenic drift produces the substrains that cause the yearly epidemics, whereas antigenic shift causes pandemics, such as the 2009 worldwide pandemic caused by the “swine flu.”

Influenza A strains are identified by the versions of HA and NA that they carry; A(H1N1) and A(H3N2) are the strains that are circulating today. Exposure to one set of HA and NA proteins provides little protection when a virus carrying a different set comes along. This is the second reason why you need to be vaccinated every year—even if immunity conveyed by the vaccine lasts long enough, the viruses may have changed since the previous year.

Despite the shortcomings of the vaccines, public health officials still recommend getting that annual flu shot. Even if not perfectly matched, the antibodies the vaccine induces can give partial protection, making the flu less severe than it otherwise would be.

Two flu strains, peaking at different times

At the start of the 2018-2019 flu season, the dominant circulating strain of virus was A(H1N1), and the flu vaccine was well matched to it.

Credit: The Conversation

The more virulent strain, A(H3N2), was present at a low level until mid-January, when its incidence started sharply increasing. At the same time, the number of people with flu-like illness, which had been decreasing, started rising again.

By mid-February, A(H3N2) was the dominant flu strain circulating, and the number of people with flu-like illness was at its peak.

The HA proteins of the many of the A(H3N2) viruses that appeared late in the season were significantly different from the HA of the virus that was used for the vaccine. There were several different substrains of A(H3N2) circulating, and the vaccine was poorly matched to over half of them.

And remember, flu immunity steadily wanes after vaccination. The effectiveness of the vaccine against A(H3N2) starts low, typically about 35%. So, by five months after vaccination, it is essentially zero. People vaccinated in September had little immunity by February to any of the circulating A(H3N3) substrains, even the one used in the vaccine.

These two factors—poor match of the vaccine to the late arising A(H3N3) viruses and waning immunity—account for the second wave of flu in the 2018-2019 season.

Hoping for a one-and-done shot

Scientists are trying to make a “universal vaccine” that would immunize against all, or most, flu strains and also give protection lasting more than one season.

Most strategies attempt to redirect the immune response away from the highly variable HA head region toward other less variable parts of HA or other less mutable viral proteins. Several of these prototypes are in clinical trials.

Not all of these proposed vaccines will prevent infection, but instead are designed to make an infection less severe. That may be the most important goal—not to prevent the flu, but to stop it from killing people.

Explore further

Why did the flu kill 80,000 Americans last year? Provided by The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Citation: This year the flu came in two waves—here’s why (2019, May 30) retrieved 2 February 2020 from https://medicalxpress.com/news/2019-05-year-flu-waveshere.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

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