Influenza (flu) – Symptoms and causes – Mayo Clinic

Overview

Influenza is a viral infection that attacks your respiratory system your nose, throat and lungs. Influenza is commonly called the flu, but it's not the same as stomach "flu" viruses that cause diarrhea and vomiting.

For most people, the flu resolves on its own. But sometimes, influenza and its complications can be deadly. People at higher risk of developing flu complications include:

Though the annual influenza vaccine isn't 100% effective, it's still your best defense against the flu.

At first, the flu may seem like a common cold with a runny nose, sneezing and sore throat. But colds usually develop slowly, whereas the flu tends to come on suddenly. And although a cold can be a bother, you usually feel much worse with the flu.

Common signs and symptoms of the flu include:

Most people who get the flu can treat themselves at home and often don't need to see a doctor.

If you have flu symptoms and are at risk of complications, see your doctor right away. Taking antiviral drugs may reduce the length of your illness and help prevent more-serious problems.

If you have emergency signs and symptoms of the flu, get medical care right away. For adults, emergency signs and symptoms can include:

Emergency signs and symptoms in children can include:

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Influenza viruses travel through the air in droplets when someone with the infection coughs, sneezes or talks. You can inhale the droplets directly, or you can pick up the germs from an object such as a telephone or computer keyboard and then transfer them to your eyes, nose or mouth.

People with the virus are likely contagious from about a day before symptoms appear until about five days after they start. Children and people with weakened immune systems may be contagious for a slightly longer time.

Influenza viruses are constantly changing, with new strains appearing regularly. If you've had influenza in the past, your body has already made antibodies to fight that specific strain of the virus. If future influenza viruses are similar to those you've encountered before, either by having the disease or by getting vaccinated, those antibodies may prevent infection or lessen its severity. But antibody levels may decline over time.

Also, antibodies against influenza viruses you've encountered in the past may not protect you from new influenza strains that can be very different viruses from what you had before.

Factors that may increase your risk of developing the flu or its complications include:

If you're young and healthy, the flu usually isn't serious. Although you may feel miserable while you have it, the flu usually goes away in a week or two with no lasting effects. But children and adults at high risk may develop complications that may include:

Pneumonia is one of the most serious complications. For older adults and people with a chronic illness, pneumonia can be deadly.

Mayo Clinic offers flu shots in Arizona, Florida and Minnesota.

The Centers for Disease Control and Prevention (CDC) recommends annual flu vaccination for everyone age 6 months or older. The flu vaccine can reduce your risk of the flu and its severity and lower the risk of having serious illness from the flu and needing to stay in the hospital.

Flu vaccination is especially important this season because the flu and coronavirus disease 2019 (COVID-19) cause similar symptoms. Flu vaccination could reduce symptoms that might be confused with those caused by COVID-19. Preventing the flu and reducing the severity of flu illness and hospitalizations could also lessen the number of people needing to stay in the hospital.

It may be possible to get a COVID-19 vaccine at the same time as your flu vaccine.

This year's seasonal flu vaccine provides protection from the four influenza viruses that are expected to be the most common during the year's flu season. This year, the vaccine will be available as an injection and as a nasal spray.

The nasal spray isn't recommended for some groups, such as:

If you have an egg allergy, you can still get a flu vaccine.

DeeDee Stiepan: Getting your annual flu vaccine is especially important this season.

Gregory Poland, M.D., Infectious Diseases, Mayo Clinic: Where we have COVID spreading, we will very likely have influenza spreading.

DeeDee Stiepan: The flu vaccine won't protect against COVID-19 but it can help reduce the chance of getting the flu.

Dr. Poland: The symptoms of COVID and influenza overlap almost exactly in their initial manifestations with the exception of the loss of smell, loss of taste. That would be very unusual in influenza.

DeeDee Stiepan: Getting a flu vaccine helps rule out influenza if you develop respiratory issues and helps reduce stress on the health care system.

Dr. Poland: Every American, age six months and older, get a flu vaccine. An opportunity we have in the context of this twindemic is not only to get our flu vaccines but to remember these non-pharmaceutical interventions: the mask wearing, physical distancing. While they prevent COVID, they also decrease the risk of influenza.

DeeDee Stiepan: For the Mayo Clinic News Network, I'm DeeDee Stiepan.

The influenza vaccine isn't 100% effective, so it's also important to take several measures to reduce the spread of infection, including:

Avoid crowds. The flu spreads easily wherever people gather in child care centers, schools, office buildings, auditoriums and public transportation. By avoiding crowds during peak flu season, you reduce your chances of infection.

Also avoid anyone who is sick. And if you're sick, stay home for at least 24 hours after your fever is gone so that you lessen your chance of infecting others.

Both COVID-19 and the flu may be spreading at the same time. Your local health department and the CDC may suggest other precautions to reduce your risk of COVID-19 or the flu if you haven't been fully vaccinated. For example, you may need to practice social distancing (physical distancing) and stay at least 6 feet (2 meters) from others outside your household. You may also need to wear a cloth face mask when indoors with people outside your household and when outdoors in crowded areas. If you're fully vaccinated and are in an area with a high number of new COVID-19 cases in the last week, the CDC also recommends wearing a mask indoors in public and outdoors in crowded areas or when you're in close contact with unvaccinated people.

Sept. 21, 2022

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Influenza (flu) - Symptoms and causes - Mayo Clinic