Flu Season

Influenza infections can actually occur at any time of year, but they’re much more common during fall and winter. Flu season varies from year to year, but it roughly begins around October, peaks around February, and tapers off in April.

It’s not just the exact timing of the season that varies. The specific varieties of flu viruses circulating are different each year, and so are rates of complications, hospitalizations, and deaths. The only constant is that the flu arrives every year — and people die from it.

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The Flu: Duration and Symptoms

Most people are sick with flu for 3 to 7 days, but some people may be ill for more than 2 weeks. These are the most common symptoms of flu, though not everyone has all of them:

  • Fever and/or chills
  • Cough
  • Muscle or body aches
  • Headache
  • Fatigue
  • Sore throat
  • Runny or stuffy nose
  • Sometimes vomiting and diarrhea (mostly in children; rarely in adults)

Differences Between Flu and COVID-19

Flu and COVID-19 are both respiratory illnesses caused by viruses that spread in similar ways. However, people with COVID-19 are contagious for a longer period and may take longer to develop symptoms of the disease. COVID-19 also has a higher likelihood of resulting in hospitalization.

“Both COVID-19 and influenza have a lot of overlapping symptoms, so fever, headaches, myalgias, or achy body and joints,” says Marian Michaels, MD, of the Division of Pediatric Infectious Diseases at UPMC Children’s Hospital of Pittsburgh. “Those kinds of things can really be seen with both influenza and COVID-19, so sometimes it’s very difficult to tell without having an actual test.

“There are a couple of things that are a little bit different between one and the other, which is worth mentioning. With COVID-19, people have seen a new onset of just not being able to smell or taste, and that’s more common with COVID-19 than with influenza. And influenza, in general, comes on a little bit faster and a little bit harder. But to really be able to know, you would have to test to tell the difference.”

COVID-19 often attacks more systems in the body than the flu. In addition to respiratory problems, COVID-19 can cause blood clots and organ failure. In the United States, around 1 to 3 out of 100 people with COVID-19 die, compared to about 1 out of 1,000 people with the flu.

The seriousness of flu infections also varies from year to year. In the 2019-2020 season, approximately 39 to 56 million people had the flu. Of these, an average of 575,000 people were admitted to the hospital, and 24,000 to 62,000 people died from flu.

How Flu Spreads

Like COVID-19, flu mostly spreads to others when an infected person releases droplets containing the virus while talking, coughing, or sneezing. Some droplets are tiny enough to be inhaled, while others land on the hands or faces of people in the area. A person may get the flu by touching something with the virus on it and then touching their mouth, nose, or eyes.

People who have a flu infection can pass it to others a day before their symptoms start. They are most contagious for the first 3 to 4 days after getting sick. But people with flu can still make others sick up to a week after getting sick.

On average, about 8 out of 100 people get sick from flu each year, though it varies from season to season. The people most likely to get flu are children. The people most likely to develop complications from flu are adults over age 65 and those with certain medical conditions.

How to Prevent the Flu

The best way to reduce your risk of flu is getting the flu shot. It takes about 2 weeks for your body to build immunity to the flu after getting the vaccine. Even if you don’t get one before flu season starts, it’s never too late to get the flu vaccine.

“This is a great time to get the vaccine,” Dr. Michaels says. “We do recommend sometime mid-September through October being an ideal time because we don’t know precisely when, this year, flu is going to come.”

The flu shot cannot give you the flu and does not increase your risk of catching COVID-19. But you may experience mild side effects for a few hours or several days after getting the flu vaccine. These include:

  • Soreness, redness, or swelling where you got the shot
  • Headache
  • Fever
  • Muscle aches
  • Feeling sick to your stomach
  • Tiredness
  • Runny nose, cough, vomiting, or sore throat from the nasal vaccine

Some people might faint or feel dizzy for an hour or two after getting the vaccine. If the dizziness doesn’t go away, tell your doctor. Serious reactions to the flu shot are very rare. But if you have trouble breathing or develop a serious rash, tell your doctor immediately.

Other ways to reduce your risk of flu include following good hygiene:

  • Regularly wash your hands, especially before and after touching your face
  • Use a hand sanitizer containing alcohol if you cannot wash your hands
  • Avoid touching your eyes, nose, and mouth as much as possible
  • Wear a face covering in public places around other people, especially indoors
  • Avoid close contact with people who are sick
  • Get plenty of sleep, eat a healthy diet, stay physically active, and drink plenty of fluids every day
Sources

2019-2020 U.S. Flu Season: Preliminary Burden Estimates, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

About Flu, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Clinical Signs and Symptoms of Influenza, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States — 2017–2018 influenza season, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States — 2018–2019 influenza season, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Flu Vaccine Safety Information, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Handwashing: Clean Hands Save Lives, Centers for Disease Control and Prevention. Link

Healthy Habits to Help Prevent Flu, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

How Flu Spreads, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Kelly Servick, How will COVID-19 affect the coming flu season? Scientists struggle for clues, Science Magazine, August 14, 2020. Link

Key Facts About Influenza (Flu), National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Key Facts About Seasonal Flu Vaccine, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

Mortality Analyses, Coronavirus Resource Center, John Hopkins University and Medicine. Link

Nicola Jones, How coronavirus lockdowns stopped flu in its tracks, Nature. May 21, 2020. Link

Seasonal Flu Shot, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

The Flu Season, National Center for Immunization and Respiratory Diseases (NCIRD), Centers for Disease Control and Prevention. Link

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