Home / Science / Health /  How long do flu symptoms last? What to know

Many people are experiencing the particular misery of the flu for the first time in several years. After two years of milder flu seasons, here is a reminder of what the flu is—and what to do if you get it.

This flu season hit earlier and harder than those of the past couple of years, doctors say. The reason is likely because of the cyclical nature of the flu and the lifting of Covid precautions such as working from home, wearing masks and having smaller social gatherings, says Robert Frenck, a pediatrician in the division of infectious diseases at Cincinnati Children’s hospital in Ohio.

We asked doctors what to expect this year if the influenza virus causes illness in your household.

Which symptoms are most common?

The hallmark symptoms of the flu are fever, headache, chills and body aches, says Dr. Frenck. Sore throat and cough are typical, too, he says.

But not everyone who has the flu will get a fever, says Ryan Mire, an internal medicine physician in Nashville, Tenn., and president of the American College of Physicians.

In children, the influenza virus can infect the digestive system and cause diarrhea, says Tochi Iroku-Malize, a family doctor in Islip, N.Y., and president of the American Academy of Family Physicians.

Symptoms of the flu tend to come on suddenly, within a day or even hours. “It is such a sudden change, they can usually pinpoint around the exact time they started to feel bad," says Dr. Mire. That is distinct from other viruses such as the common cold, where symptoms tend to come on more gradually, he says.

And unlike a cold, you’re less likely to be able to power through symptoms. “You feel terrible," says Dr. Frenck. “You just want to get in bed and pull the covers over your head."

How long do flu symptoms last?

On average, the crushing fever, chills and body aches tend to last between three and five days, says Dr. Frenck. But fatigue and cough can linger for up to three weeks, he says.

Dr. Mire notes that the trajectory of flu is highly individual and unpredictable.

“I’ve had people feel better after 72 hours and patients who have felt really bad and could not go to work for almost two weeks," he says. Whether you’ve had your flu shot, how robust your immune system is and how big of a dose of the virus you got can all influence how intense your symptoms are and how long they persist.

Why can flu symptoms last so long?

People with the flu can start to feel better and then take a turn for the worse, often between days 10 and 14, says Dr. Frenck.

For those who have this worsening of symptoms, it may signal a secondary bacterial infection, such as pneumonia. Pneumonia is often characterized by a return of fever and a worsening cough, sometimes accompanied with difficulty breathing. People can also develop ear or sinus infections or even encephalitis, which occurs when the influenza virus gets into the spinal fluid and can cause confusion and other symptoms, says Dr. Mire.

Dr. Iroku-Malize says that if you’re having any trouble breathing, are unable to eat or drink, or if you’ve been improving and then symptoms worsen, see your doctor.

It is secondary infections, particularly pneumonia, that are often what land people in the hospital and can lead to flu deaths, doctors say. Secondary bacterial infections from influenza need to be treated with antibiotics.

For how long are you contagious when you have the flu?

People shed the flu virus for about four to five days, says Seema Lakdawala, associate professor of microbiology and immunology at Emory University School of Medicine who studies influenza transmission.

But the tricky thing with flu is that you are contagious starting about 24 hours before you show symptoms, says Dr. Lakdawala.

Fever is associated with high viral loads, says Dr. Mire, so people are highly contagious while they have a fever. He advises his patients to stay home until they are fever-free, without using any fever-reducing medications, for at least 24 hours. After that, they are much less likely to be contagious.

Dr. Lakdawala notes that since the H3N2 version of flu that is circulating this year is more commonly transmitted via close contact, wearing masks, increasing ventilation and social distancing will cut the possibility of spreading the virus.

People generally will become infected about one to two days after being exposed to the influenza virus. “If you don’t have any symptomatic onset within three to four days [of being exposed to someone with the flu], you’re probably in the clear," she says.

How is the flu treated?

Other than rest and fluids, doctors recommend treating the individual symptoms. For fever and body aches, for example, Dr. Iroku-Malize says your doctor may recommend acetaminophen and ibuprofen. Some people get relief from congestion from mentholated topical rubs, she says.

Antiviral medications such as Tamiflu can cut the duration of flu symptoms by a day or two. The drugs also reduce the risk of complications such as secondary infections and hospitalization. Doctors recommend antivirals for people at high risk for flu complications including people aged 65 and older and those with chronic health conditions such as diabetes and heart disease. Taking antivirals within the first 48 hours of symptoms is most effective, says Dr. Mire. The most common side effect of the drugs is nausea and vomiting.

If you have symptoms of flu and are at increased risk of complications, it is important to get tested for flu so you can get a diagnosis and start treatment in time for antivirals to be most effective.

Is there anything else I can do to lessen my odds of getting the flu?

Doctors emphasize the importance of getting your flu shot, which reduces the risk of infection and of complications if you do catch the virus. The vaccine is particularly important for older adults, young children, pregnant women and people with other health conditions.

And it isn’t too late to get your shot this year, says Dr. Frenck. He notes that flu activity is typically highest in January and February. Also, two main types of flu circulate, type A and type B. Even if you’ve already had the flu recently, you can still get the other type, he says.

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