Key takeaways

The flu virus is primarily spread through droplets from an infected person’s sneeze, cough, or speech, but evidence suggests it can also be airborne, necessitating masks and social distancing as prevention measures.
Flu season peaks between December and February, with vaccination being a crucial tool for prevention, despite the flu virus’s ability to change from year to year.
An infected person can spread the flu one day before symptoms appear and up to seven days after, with the most contagious period being three to four days after symptoms start.
Preventative measures include getting vaccinated annually, maintaining COVID-19 safety protocols, practicing good hygiene, and staying home when sick to reduce the spread of the flu.

Transmission | Flu season | Contagiousness | How to stop the spread

The influenza virus (aka, “the flu”) is kicking around all year long. But things really start to amp up when the weather turns cool. Fall and winter are prime flu season months, with cases of the contagious respiratory illness peaking between December and February. With the novel coronavirus (COVID-19) and the flu on a collision course, this could be “the worst fall, from a public health perspective, we’ve ever had,” Robert Redfield, MD, director of the Centers for Disease Control and Prevention (CDC) said in a widely circulated WebMD interview.

The flu is more than just a cold on steroids. It comes on suddenly and can produce a fever, chills, fatigue, headache, body aches, vomiting, and diarrhea—in addition to symptoms often associated with the common cold, like a sore throat, sneezing, cough, and runny nose. The CDC estimates that between 39 to 56 million people in the United States were infected with the influenza virus between Oct. 1, 2019 and April 4, 2020, with 24,000 to 62,000 dying.

Preventing the flu is more important than ever, thanks to the coronavirus pandemic and an already-burdened healthcare system. Sure, vaccination is key. But knowing when and how the flu virus is transmitted are important tools in keeping you and your family flu-free this season.

Is the flu airborne?

Experts believe that the flu is primarily spread through the droplets released when an infected person sneezes, coughs, or speaks. These droplets land in the mouths or noses of people nearby. Or, less commonly, a person might touch a surface contaminated with them, then touching his or her own face.

But now there’s evidence showing that influenza transmission can also be airborne. A 2018 study out of the University of Maryland and published in the journal Proceedings of the National Academy of Sciences of the United States of America found that the flu virus can be shed in tiny droplets suspended in the air from the exhaled breaths of infected people. How far these infectious aerosols travel and how long they stay in the air wasn’t studied, but standard COVID-19 safety protocols—standing six feet away from people and wearing a face or surgical mask—may be good infection-control measures in addition to handwashing.

And while you may have heard a lot about how limiting our exposure to germs weakens the immune system, some healthcare professionals say it’s not something we need to be concerned about in the short term, as we fight the COVID-19 pandemic. “I can see all these measures decreasing the immune response, especially in the very young, who are building up their repertoire of memory cells,” says Hilary Smith, MD, a pediatrician affiliated with Boston Children’s Health Physicians. “But I’d rather take my chances killing some good germs [along with] the coronavirus.”

Whether it’s droplets or aerosols, another thing to consider when it comes to catching any germ is one’s own individual immune system. “Why does the flu always hit the very old and the very young particularly hard?” Dr. Smith asks. “It’s because of their [weaker] immune systems, to a degree. As a pediatrician, I can get coughed and sneezed on by kids with the flu all the time and in the 14 years I’ve been practicing, I haven’t caught the flu. Is that all because I got the flu shot? No. A lot of it just depends on your immune system.”

When is flu season?

You can catch the flu at any time of year, but cases tend to tick upward starting about October, peaking around February, and then dropping (although not disappearing) in the spring and summer.

Vaccination is an important tool against the spread of the flu, but what worked last year might not work this year. That’s because the flu virus itself can change from one year to the next.

“Influenza viruses replicate in human and animal cells using a process that easily allows changes to its genetic material,” explains Robert Hopkins Jr., MD, a professor of internal medicine at the University of Arkansas for Medical Sciences. “This results in a constant shift in virus characteristics and, less frequently, major changes that can lead to pandemics. There’s active research ongoing to develop a ‘universal’ flu vaccine to protect us by attacking parts of the virus which remain more stable despite these genetic ‘errors.’ The vaccine we will use this year has three major changes from the type we used last year—again, it’s a guess—but I am hopeful it will be very effective.”

How will COVID-19 affect this year’s flu season? Will more people social distancing and wearing face masks help tamp down the spread of the flu? Or will people, wary of making a trip to their doctor’s office where COVID-19 patients might be, forgo the flu shot? Only time will tell.

“Unfortunately, our experience with COVID has demonstrated that our society, as a whole, is not very good at personal-protection activities,” comments Dr. Hopkins. “While I would love to see a significant uptick in influenza vaccination acceptance this year—and I will certainly push for that—I expect this to be a difficult winter with the convergence of COVID and flu along with RSV [respiratory syncytial virus, a common and contagious respiratory infection usually seen in young children], which also causes significant respiratory illness in the winter.”

How long is the flu contagious?

According to the CDC, an infected person can start spreading the flu virus one day before symptoms arise and up to seven days after. Overall, though, an infected person is most contagious three to four days after their symptoms start. Children and people with a weakened immune system (for example, those with certain immune diseases like rheumatoid arthritis, lupus, and people on chemotherapy) can be contagious for longer than seven days.

Most people recover from the flu and are no longer contagious after about a week. Staying home and away from people while you recuperate is important to stopping the flu’s spread. Experts at UC-Irvine Health say you should stay home until:

You have no fever for 24 hours (without taking fever-reducing medicines like aspirin, acetaminophen (Tylenol), or ibuprofen (Advil or Motrin)
You do not have vomiting or diarrhea for at least 24 hours
Your coughing and sneezing has been reduced by at least 75%

And don’t push yourself. Ease back into your normal routine gradually. If just getting up, showered, and dressed exhausts you, you probably should stay home and continue to rest. Experts advise not returning to your normal schedule until you have at least 90% of your regular energy levels back.

How to avoid spreading the flu (and how to protect yourself)

Getting the flu this winter isn’t inevitable. There are safety precautions you can (and should) take.

1. Get vaccinated annually.

The influenza vaccine is available at pharmacies and in healthcare settings, such as your doctor’s office or local health clinic.
Flu vaccination is recommended for most people ages 6 months and older.
Vaccination is particularly important for people who have a high risk of complications from the flu, including young children, those over 65, and those with certain health conditions like asthma or diabetes.
The vaccine isn’t always a perfect match against a changing flu virus, but according to the CDC, it typically reduces the risk of flu by 40%-60%.
The best time to get vaccinated is in September or October, before the flu season kicks into high gear. But getting vaccinated into the winter can still be worthwhile.
And let’s set the record straight: The flu vaccine won’t give you the flu, although you could develop some mild side effects, like a fever and muscle aches.

2. Keep up your COVID-19 protection measures. These measures are particularly helpful if you’re taking care of someone with the flu.

Wear a face mask.
Stay six feet apart from people. Research published in the Journal of Infectious Diseases found that 89% of flu viruses were found in small particles that circulated up to six feet from an infected person’s head. The closer you were to the person, the higher the concentration of the virus.
Wash your hands (for 20 seconds) regularly or use hand sanitizer with at least 60% alcohol. If you’re caring for a sick person, it’s especially important to wash your hands after handling the person’s used tissues and dirty laundry and dishes/cups.
Clean frequently touched surfaces (doorknobs, keyboards, counters/desks/tables) with disinfectants regularly. According to the CDC, the flu virus can live on surfaces for up to 48 hours. Common household cleaners, such as detergents and cleaners containing alcohols or hydrogen peroxide are effective cleaners, says the CDC.

3. If you sneeze or cough, do so into a tissue or your elbow and then wash your hands or use hand sanitizer.

4. Avoid touching your nose, mouth, or eyes—easy entry points for the flu virus.

5. Again, stay home if you feel sick and don’t return to your normal activities until you are well.

With these measures, you reduce your risk of becoming sick, and the potential for complications if you do catch the virus.