Everything to Know About the Flu, Including How Long It’s Actually Contagious
Flu cases are starting to creep up across the country. With that, it’s understandable to have questions, including “How long is the flu contagious?”
It’s a good idea to at least be aware of some flu basics (is it a cold, the flu, or COVID-19?) since public health experts say we could be in for a nasty flu season.
CDC director Rochelle Walensky warned in an interview with NBC News earlier this month that this flu season could be intense. “Not everybody got flu vaccinated last year, and many people did not get the flu. So that makes us ripe to have potentially a severe flu season,” she said.
Infectious disease expert Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security, predicts that this flu season “will be more reminiscent of pre-COVID influenza seasons.” Meaning, cases will be higher than we’ve seen recently. The actual timing of flu season has been thrown off due to the pandemic, he points out. “It is still hard to tell when it will begin in earnest and if its seasonality will be altered—last season it went into June,” he notes.
“It looks like we’re going to have an early flu season based on some numbers we’ve seen so far,” says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. “Package that together with the fact that the southern hemisphere—which usually predicts what will happen here—has an intense flu season, and it could be bad.”
Flu season has slowly gotten worse since 2020, when cases were practically non-existent due to pandemic lockdown measure. But there were an estimated 9 million flu illnesses, 4 million flu-related medical visits, 100,000 flu-related hospitalizations, and 5,000 flu deaths last year, according to the Centers for Disease Control and Prevention (CDC).
Given that the past few years have made everyone stop and think about how we catch and pass on illnesses, it’s only natural to wonder how long the flu is contagious—especially if you’re unlucky enough to get it. Curious about when you can safely be around others after having the flu? Here’s what you need to know.
How long is the flu contagious?
There’s a spectrum here. People with the flu are most contagious in the three to four days after they develop symptoms, the CDC says. Most people can infect other people up to a day before their symptoms start and up to five to seven days after they show signs of the virus. Kids and people with weakened immune systems may be able to pass on the virus for more than seven days.
But there are a few variables that come into play. “Contagiousness for an infectious disease is not an on and off switch,” Dr. Adalja says. “But it’s important to remember that, as you get further out from when your symptoms started, you could still be contagious.”
Things like taking oseltamivir (Tamiflu) and being vaccinated against the flu should also shorten the amount of time you’re sick—and infectious, Dr. Russo says. Baloxivir (Xofluza) “does likely diminish contagiousness as seen in household attack rate studies,” Dr. Adalja says. One study published earlier this year, for example, found that other family members got the flu 9.5% of the time when a patient took baloxivir compared to the 19% when the patient took oseltamivir.
Still, Dr. Russo says, “I like to consider people infectious up to seven days, just to be safe.”
As a whole, “people are generally most contagious one to four days after they fall ill,” says David Cennimo, M.D., assistant professor of medicine- infectious disease at Rutgers New Jersey Medical School. “This time of maximal infectivity generally coincides with the time of the worst symptoms [and] most household infections happen right away,” he adds.
What is the flu, again?
The flu (aka influenza) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs, according to the CDC. There are two main types of flu viruses—types A and B—and they usually circulate during flu season every year.
The flu can cause the following symptoms, per the CDC:
fever or feeling feverish/chills
cough
sore throat
runny or stuffy nose
muscle or body aches
headaches
fatigue
Vomiting and diarrhea (this is more common in children than adults)
How does the flu spread?
The flu is thought to mainly spread by droplets that are created when an infected person coughs, sneezes, or talks. Those droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into their lungs, the CDC explains. Less commonly, a person could get the flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or eyes.
How to keep from spreading the flu
If you have the flu and you’re able to isolate, Dr. Adalja recommends doing just that. That means you should try to sleep apart from other members of your household and use a different bathroom, if you have one. You should stay in isolation until you’re fever-free for 24 hours, Dr. Adalja says. And, if you need to be around others, he suggests wearing a high-quality mask to lower the risk you’ll infect them.
“The same things that work with COVID should work with the flu,” Dr. Russo says. If it’s within seven days since you were diagnosed and you’re out and about, Dr. Russo recommends wearing a mask to help lower the risk you’ll spread the virus to others. “That’s particularly true if you’re interacting with vulnerable people,” like the elderly, very young, or pregnant people, he says.
“I’m hoping that people will be considerate of others and do what they can in terms of minimizing risk of spreading the flu to others if they get infected,” Dr. Russo says. “Influenza is still a lethal virus.”
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