How Long Are You Contagious With the Flu?

Think of how easily juicy gossip spreads from person to person. In many ways, the flu virus works the same way ― which explains how it manages to infect a billion people a year around the world.

Influenza is a contagious, infectious disease that continually circulates through the global population. The virus keeps moving because of … well, all of us.

The process is simple: We get the flu virus. We share the flu virus. We repeat the process.

But that doesn’t mean that we’re powerless to slow the respiratory illness. Knowing when you start being contagious with the flu and how long you’re contagious allows you to take precautions to not infect others.

For more on flu germs, we turn to infectious disease doctor Sherif Mossad, MD.

How contagious is the flu?

“Highly” is the answer to that question. The flu can spread extremely quickly through a large group once the virus arrives on the scene. (Think of your office, for example, or your child’s school.)

People with the flu can spread the ickiness to anyone within 6 feet of them, notes Dr. Mossad. The virus is typically delivered through droplets sent airborne when people cough, sneeze or simply talk.

Sometimes, people can be infected with the flu and share the virus without showing any symptoms of the illness.

When are you contagious with the flu?

If you get the flu, it usually takes two days to start showing the classic symptoms such as a fever, chills, cough and headache. Sometimes, it can take up to four days for symptoms to appear.

You can start spreading the virus during that waiting period.

“You may be contagious with the flu beginning about a day before you feel symptoms ― meaning you can spread it to others before you know you’re sick,” explains Dr. Mossad.

You’ll be most contagious with the flu during the first three or four days after you feel ill. Germs may still be shared for a week after symptoms start, too. (Children and adults with weakened immune systems may be contagious even longer.)

“That’s why keeping your distance from others for several days after you get sick is important,” he adds.

How long should you isolate with the flu?

A good rule of thumb is to stay home from work or school until you’ve been fever-free for at least 24 hours without using fever-reducing medications like acetaminophen (Tylenol®) or ibuprofen (Advil®), notes Dr. Mossad.

A fever is defined as:

• Higher than 100.4 degrees Fahrenheit (or 38 degrees Celsius) in adults.
• Higher than 100.4 F (38 C) in children, if measured rectally.
• Higher than 99.5 F (37.5 C) in children, if measured orally.
• Higher than 99 F (37.2 C) in children, if measured under an arm.

You should also stay home if you have other severe symptoms, such as a nonstop cough or shortness of breath. (This should be obvious, but if you’re showing signs of being sick, you probably still are.)

The timeframe for returning to work or school activities may also depend on your job and how frequently you interact with people. Many organizations have specific guidelines for when you can go back. Check for any procedures.

How does the flu spread?

The flu spreads when tiny droplets of virus-laden particles are exchanged between people.

“The main way people infect each other with flu is being in close proximity,” clarifies Dr. Mossad. “An infected person coughs or sneezes and tiny drops of fluids get on your face or hands ― and eventually, those virus-filled particles get in you.”

And once you’re infected, you can start passing the flu to others within about 24 hours to continue the spread.

How can you prevent the spread of the flu?

To avoid the virus and stay healthy during flu season, Dr. Mossad suggests a multipronged approach for protection.

Get your flu vaccine

The first and most important step in preventing flu is to get a flu vaccine each year.

“The flu shot is your best defense against the flu,” Dr. Mossad stresses. “Studies tell us that if you get the flu vaccine, you are much less likely to have a severe illness and much less likely to be hospitalized.”

Influenza annually causes 3 million to 5 million cases of severe illness around the world, according to the World Health Organization (WHO). It also leads to 290,000 to 650,000 respiratory deaths a year.

Wash your hands

Whether you realize it or not, you probably touch your face an average of 23 times an hour. Now imagine all the potentially germy things you’ve touched since the last time you washed your hands. Ick, right?

Washing your hands is the No. 1 way to keep viruses from elbowing their way into your body and making you sick. There’s a long list of instances when it’s appropriate to wash your hands, but these are particularly important during flu season:

• Before and after contact with an ill person.
• After blowing your nose, coughing or sneezing. (Wash your hands more often when you’re sick to prevent spreading your germs to those around you, too.)
• Every time you come home after being out.
• Before eating or preparing food.

Wash your hands thoroughly for about 20 seconds with soap and water. If you aren’t able to use soap and water, use an alcohol-based hand sanitizer.

Everyday preventive measures

Limit your opportunities for being infected by:

• Avoiding being around people who are sick whenever possible.
• Keeping your hands away from your eyes, nose and mouth.
• Eating well, exercising and getting enough rest.
• Considering a multivitamin and possibly vitamin D supplements to support your immune system. (Ask your healthcare provider if you think you would benefit from supplements.)

And if you don’t feel well, stay away from other people to help them stay healthy.

Getting flu treatment

Even if you take every possible precaution, you may still get the flu. (It is a rather persistent virus.) Call a healthcare provider as soon as possible when symptoms start.

“There are medications your doctor can give you early to help lessen the effects of the flu,” says Dr. Mossad. “But if you wait, chances are you’ll be through the worst of your symptoms and the medication isn’t going to be as helpful at that point.”

Then, make sure to stay home and get some rest while keeping your germs to yourself.