What Is the Flu?

Influenza — what most of us call "the flu" — is a contagious viral infection of the nose, throat, and lungs. It can make a person feel very sick.

When Should People Get the Flu Vaccine?

Flu viruses usually cause the most illness during the colder months of the year. In the United States, flu season is from October to May.

It's best to get the flu vaccine early in flu season, ideally by the end of October. This gives the body a chance to make antibodies that protect it from the flu. But getting a flu vaccine later in the season is better than not getting it at all. Getting a missed flu vaccine late in the season is especially important for people who travel. That's because the flu can be active around the globe from April to September.

Who Should Get the Flu Vaccine?

The Centers for Disease Control and Prevention (CDC) recommends a flu vaccine for everyone 6 months of age and older.

Babies younger than 6 months can't get the vaccine. But if their parents, other caregivers, and older kids in the household get it, that will help protect the baby. This is important because infants are more at risk for serious problems from the flu.

How Is the Flu Vaccine Given?

• Kids younger than 9 years old who get the flu vaccine for the first time or who've had only 1 dose of the vaccine before July 2023 will get 2 doses at least 1 month apart.
• Kids younger than 9 who got at least 2 doses of flu vaccine before July 2023 will only need 1 dose.
• Kids older than 9 need only 1 dose of the vaccine.

Talk to your doctor about how many doses your child needs.

Where Can My Family Get the Flu Vaccine?

The flu vaccine usually is available at:

• doctors' offices
• public, employee, and university health clinics
• most drugstores
• some supermarkets and big-box stores
• some community groups or centers
• some schools

What Are the Types of Flu Vaccines?

Two types of flu vaccine are available:

• the flu shot, which is injected with a needle
• the nasal spray, a mist that gets sprayed into the nostrils

Both protect against the four types of influenza virus that are causing disease this season.

In the past, the nasal spray vaccine wasn't recommended for kids because it didn't seem to work well enough. The current version appears to work as well as the shot. So either vaccine can be given this year, depending on the child's age and general health.

The nasal spray is only for healthy people ages 2–49. People with weak immune systems or some health conditions (such as asthma) and pregnant women should not get the nasal spray vaccine. It should also be avoided in kids who take aspirin regularly, who have a cochlear implant, or who have recently taken antiviral medicine for the flu.

Why Is the Flu Vaccine Recommended?

While the flu vaccine isn't 100% effective, it still greatly lowers a person's chances of catching the flu, which can be very serious. It also can make symptoms less severe if someone who got the vaccine does still get the flu.

If you got the flu vaccine last year, it can't provide enough protection this year, because flu viruses change. That's why the vaccine is updated each year to include the most current types of the virus.

Sometimes the same virus types are included in the vaccine from one year to the next. Even then, it's still important to get the yearly flu vaccine because the body's immunity against the influenza virus declines over time.

Getting the flu vaccine not only protects you from the flu. It also helps protect the people and community around you. The flu vaccine makes someone less likely to get the flu, and therefore less likely to spread the flu. Getting the flu vaccine is a great way to protect people who are at risk from flu, such as the elderly, babies, and people with health conditions such as asthma. Every year thousands of people die from influenza, and getting the flu vaccine is one way to help prevent that.

What Are the Possible Side Effects of the Flu Vaccine?

Both types of vaccine can cause mild side effects.

• The flu shot usually is given as an injection in the upper arm or thigh (depending on a person's age). It contains killed flu virus and can't cause someone to get the flu. But it can cause soreness, redness, or swelling at the injection site. Rarely, it might cause a low fever or body aches.
• The nasal spray flu vaccine contains weakened live flu viruses. So it may cause mild symptoms, such as a runny nose, wheezing, sore throat, vomiting, or tiredness. Like the shot, it can sometimes cause a low fever or body aches.

Sometimes, people faint after getting a shot, especially teens. It helps to sit or lie down for 15 minutes right after a shot to prevent this.

If your child has any side effects, talk to your doctor about giving either acetaminophen or ibuprofen and to find out the right dose.

A warm, damp cloth or a heating pad on the injection site may help ease soreness, as can moving or using the arm.

Very rarely, the flu vaccine can cause a serious allergic reaction.

What Else Should I Know?

Some things might prevent a person from getting the flu vaccine. Talk to your doctor to see if the vaccine is still recommended if your child:

• has ever had a severe allergic reaction to a flu vaccination
• has had Guillain-Barré syndrome

Egg Allergy and the Flu Vaccine

In the past, people with an egg allergy had to check with their doctor about whether the flu vaccine was OK for them because it's grown inside eggs. But health experts now say that the amount of egg protein in the vaccine is so tiny that it's safe even for kids with a severe egg allergy. People with egg allergies can now get the flu vaccine just like everyone else. They do not need to take any extra precautions.

COVID-19, RSV, and the Flu Vaccine

During the COVID-19 pandemic, fewer people got infected or were hospitalized with viral respiratory infections like the flu and RSV. This was probably tied to public health measures (like wearing masks in public and social distancing) that protected against COVID-19, as they also worked against other respiratory viruses. As these precautions happen less, the rate of respiratory infections in fall and winter has gone back up. And they seem to be showing up earlier and lasting longer than they did before the pandemic.

So it's more important than ever to get a flu vaccine and an updated COVID-19 vaccine. Babies (and some toddlers) also should get the RSV vaccine shot just before or during RSV season (usually fall to spring in U.S.) if their mother didn’t get the vaccine in her third trimester of pregnancy.

People can get a flu vaccine at the same time they get the COVID-19 and RSV shots. Kids who are sick with a respiratory infection should get their vaccines after they feel better. This helps prevents confusion about whether any symptoms are from the illness or are reactions to a vaccine. Also, a stuffy runny nose can make it harder for the nasal spray flu vaccine to work.

When Should I Call the Doctor?

Call your doctor if:

• Your child is sick and has a fever, and you aren't sure whether to reschedule the vaccine.
• Your child has problems after the immunization, such as an allergic reaction or high fever, or if you have other concerns.