We all know the flu can spread like wildfire.
Case in point: If you lived in the same house as someone with the flu during the 2021-2022 flu season, you had a 50 percent chance of contracting the virus yourself, according to a January 2023 JAMA study.
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So if you or someone you know is sick, exactly how long does the contagious period last? Though it's hard to pinpoint a precise answer, there are some general guidelines to keep in mind to help stop the spread. Here's what you should know.
How the Flu Spreads
The flu is a viral respiratory illness that's mainly spread by close contact with an infected person, according to the Centers for Disease Control and Prevention (CDC).
People with the flu expel tiny, germ-filled droplets when they cough, sneeze or even talk. When those droplets land in the mouth or nose of another person, they're at risk for becoming infected too.
The droplets can also land on surfaces (like doorknobs, TV remotes or keyboards, for example). If a healthy person touches the infected surface and then touches their mouth, nose or eyes, they could get sick.
You can't always avoid these droplets when you're around someone with the flu. But there are steps everyone can take to help prevent the virus from spreading. The CDC recommends you:
- Avoid close contact with people who are sick, and limit contact with others when you're sick.
- Cover coughs and sneezes with a tissue, and throw the tissue in the trash when you're done with it.
- Wash your hands often with soap and water. Use an alcohol-based hand sanitizer when soap and water aren't available.
- Avoid touching your eyes, nose and mouth as much as possible.
- Clean and disinfect surfaces that may be contaminated with the flu virus.
- Stay home for at least 24 hours after your fever has subsided.
- Get your annual flu shot each fall.
- Take flu antiviral drugs (like Tamiflu) if your doctor prescribes them.
How Long Does Influenza Last?
A bout of the flu can last for a few days or a few weeks. Often, people who've gotten a flu shot will get over their infection a little faster compared to people who weren't vaccinated, per Harvard Health Publishing.
Flu symptoms like a fever, chills or body aches often come on suddenly, peak and then slowly subside. (The average flu incubation period, or the period of time between exposure to the virus and the appearance of symptoms, is two days.)
"The second through the fourth days are usually the worst," says Nikhil Bhayani, MD, an infectious disease physician with Texas Health Resources in Bedford, Texas.
You'll know you're nearing the end of the flu when your fever has gone down (without taking any medicine) and your body isn't as achy. "That usually means the virus is controlled," Dr. Bhayani says.
So, How Long Is the Flu Contagious?
An infected person can spread the flu a day before their symptoms actually start. So, if the average incubation period is two days, you might be contagious a day or so after exposure to the flu virus.
You're most contagious during that peak symptom period, around days two through four, the Cleveland Clinic notes. But you can keep on spreading the virus until your symptoms clear up altogether.
In other words, typically you're no longer contagious with the flu once your symptoms have completely gone away, Dr. Bhayani says.
Taking an antiviral medication like Tamiflu can shorten the duration of your flu symptoms, and in turn cut down on the amount of time you're contagious by a day or two, he adds.
But even if you're experiencing mild symptoms, you can still spread the virus.
Keep in mind that taking over-the-counter meds that simply lower your fever (like ibuprofen or acetaminophen) won't actually help you get over the flu faster or make you less contagious. They just make you more comfortable while you're dealing with flu symptoms, per the Cleveland Clinic.
When to See a Doctor
Most people don't need to seek medical attention for the flu, especially if you're healthy otherwise. But it's a good idea to reach out to your doctor if you or your loved one is at high risk for flu complications like pneumonia, according to the Mayo Clinic.
That includes people under 12 or over 65, pregnant people, people with chronic medical conditions, people with a weakened immune system, people with a BMI over 40 and people living in a nursing home or care facility. In that case, your doctor might prescribe an antiviral medication like Tamiflu to help keep your symptoms in check.
Seek emergency medical care if you or your loved one are experiencing concerning symptoms, such as:
- Trouble breathing
- Chest pain
- Dizziness or confusion
- Bluish lips or face
- Severe weakness
- Symptoms that get worse after getting better
- Fever over 104 degrees Fahrenheit
Here's some more important info on the flu and how to stay healthy.
Is the flu a virus?
Yes. The flu is a viral respiratory illness caused by the influenza virus. There's no cure for viral illnesses — for most people, they simply need to run their course, per the National Library of Medicine. If you're at high risk for complications from the flu, your doctor might prescribe antiviral medications to shorten the duration and severity of your symptoms.
Are fevers contagious?
Fevers themselves aren't contagious. But they're a sign your body is experiencing an illness that could be contagious, like the flu.
"Fever could correlate to viral burden," Dr. Bhayani explains. "In essence, the immune system is in an all-out battle to fight the virus as your cells produce inflammatory markers that cause fever."
Experts recommend staying home and limiting contact with other when you have a fever. Once your temperature goes back to normal (without taking fever-reducing meds), it's safe to assume that your body has fought off the illness and that you're no longer contagious, says the Cleveland Clinic.
Can you get the flu twice in one season?
It's possible, but unlikely, Dr. Bhayani says. Multiple strains of the flu typically circulate at the same time, so you could potentially catch one strain and then catch another later in the season.
Getting a flu shot can help you stay protected, though. "Usually the influenza vaccine contains several predominant strains for the upcoming flu season," which can help reduce your chances for getting sick, says Dr. Bhayani.
- JAMA: "Household Transmission of Influenza A Viruses in 2021-2022"
- Centers for Disease Control and Prevention: "Key Facts About Influenza (Flu)"
- Harvard Health Publishing: "How long does the flu last?"
- Cleveland Clinic: "Flu (Influenza)"
- Mayo Clinic: "Flu symptoms: Should I see my doctor?"
- National Library of Medicine: "Viral Infection"
- Cleveland Clinic: "Is My Kid Contagious (and Should I Keep Them Home From School)?"
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Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.