- The flu is highly contagious.
The flu virus is most contagious in the first three to four days after you get it, even if symptoms haven't appeared yet.
- The flu is no longer contagious once your temperature has returned to normal and you're fever-free for at least 24 hours.
- This article was reviewed by Tania Elliott, MD, who specialises in infectious diseases related to allergies and immunology for internal medicine at NYU Langone Health.
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No one wants to get the flu, but every year, starting around October, the number of seasonal influenza cases begin to climb in the US. Here's what you need to know about the flu virus, which is highly contagious.
Yes, the flu is contagious
The flu is caused by a virus. According to the Centers for Disease Control and Prevention, there are four types of influenza virus: A, B, C, and D. And all four types are contagious.
Type D only really affects cattle, and type C causes only mild infections. So types A and B are the ones you need to worry about. Of those two types, there are dozens of different subtypes of type A and a couple of different strains of influenza B.
These different types don't all circulate at the same time. But they're all contagious, and they all spread the same way: through droplets dispersed by sneezing, coughing, or even talking. In fact, those droplets can spread through the air as far as six feet away.
So, if you're trying to avoid getting the flu, it's best to avoid human contact with others may have it.
The flu is most contagious in the first 3 to 4 days
Typically, you're the most contagious in the first three to four days of your illness. But that doesn't necessarily mean it's when you start showing symptoms.
"The problem is that you're actually contagious the day prior to becoming symptomatic," says Jessica Grayson, MD, an assistant professor in the department of otolaryngology at the University of Alabama at Birmingham.
That means you can spread the virus before you even know that you've contracted it - before your temperature rises and your muscles and joints start to ache.
"You can be sneezing and not thinking about covering your mouth or touching surfaces or wiping them down, and you're spreading it before you even knew that you could," says Grayson.
And after you start feeling sick, you'll remain contagious for about a week, or possibly longer if you have a weakened immune system.
You're no longer contagious if your fever is gone for 24 hours
Once your temperature has returned to normal and you're fever-free for at least 24 hours without taking any fever-reducing medication, you're unlikely to be contagious any longer.
But since the most common way to spread the flu is by coughing and sneezing up those mucusy droplets, you should always consider hygiene and what Maragakis calls "respiratory etiquette."
"Respiratory etiquette is covering your coughs and sneezes, using tissues, and coughing into your elbow instead of your hands," she says.
A couple of other tips that can help you avoid spreading the flu: Be vigilant about washing your hands - the right way - and use hand sanitiser. And improve your odds of avoiding the flu altogether by getting a flu vaccine.