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Flu Vaccines: What You Need to Know

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A typical U.S. flu season sickens millions of people, sends hundreds of thousands to the hospital, and causes thousands of flu-related deaths.

 The 2024–2025 flu season was especially tough, with hospitalization rates reaching their highest level in more than a decade.

Even if the flu (also called influenza) doesn’t result in serious complications, it can mean days of feeling miserable, missing work or school, and canceling plans.

The best way to avoid the flu or prevent serious flu illness is to get an annual flu vaccine.

There are two main forms of flu vaccine: shots and a nasal spray. Both train the immune system to recognize and fight off influenza should there be a later exposure.

Because flu viruses change quickly, the vaccine is updated every season to target the strains expected to circulate.

All flu vaccines for the 2025–26 flu season are trivalent vaccines, which means they protect against three different influenza viruses, including two influenza A viruses and an influenza B–Victoria virus.

Flu Shot Uses inactivated (killed) influenza viruses or pieces of the virus, such as proteins found on its surface. Approved for everyone 6 months and older, with a few rare exceptions.

Nasal Spray Flu Vaccine Contains live, weakened viruses that prompt an immune response without causing illness. Approved for people ages 2 through 49 who are not pregnant and do not have certain medical conditions.

Recommendations for the 2025–2026 flu vaccine are the same as in previous years: Everyone 6 months old and up, with rare exceptions, should get the annual vaccine.

A single dose is advised each flu season for most people, with some children needing two doses for best protection.

Vaccination is especially important for certain vulnerable groups:

Seniors People 65 and older are at higher risk for developing flu complications.

Young Children Kids under 5, especially those under 2, and those with medical conditions such as asthma and diabetes are particularly vulnerable to severe flu-related issues.

Pregnant People Immune system changes during pregnancy increase the risk of becoming seriously ill from the flu. Vaccination can also prevent fetal health problems and protect an infant after birth. This is especially important since babies can’t get a flu vaccine until they are 6 months old.

People With Certain Medical Conditions Chronic conditions such as COPD, asthma, heart disease, and obesity as well as disorders related to the liver, blood, and endocrine system increase the risk of severe illness or death due to the flu. In recent flu seasons, 9 out 10 people hospitalized with the flu had at least one underlying condition.

Individuals With Weakened Immune Systems Immune issues increase the risk of flu complications. The following can weaken the immune system:

  • HIV or AIDS
  • Some cancers such as leukemia
  • Cancer treatment, including chemotherapy and radiation
  • Chronic conditions that require chronic corticosteroids or other drugs that suppress the immune system.
Virtually everyone should get an annual flu vaccine, experts say. The exceptions:

  • Children younger than 6 months
  • People who have life-threatening allergies to the flu vaccine or any of its components, including gelatin or antibiotics (extreme allergic reactions to flu vaccines are very rare)
  • Some people who have had a rare nerve disorder called Guillain-Barré syndrome (GBS)

In general, experts recommend getting the flu shot in September or October. This allows for the strongest immunity against the virus when it’s typically at its peak, in December and January, and when exposure risk is highest due to holiday travel and gatherings.

But convenience and opportunity also matter. For some people, trying to optimize timing may inadvertently result in not getting the vaccine at all.

While planning when to get your flu vaccine, remember it won’t be fully effective for two weeks.

Preliminary estimates for last year’s flu season found that the vaccines were 41 to 78 percent effective against hospitalization, and 32 to 60 percent effective against less serious infections that sent a person to seek outpatient care.

There are a number of reasons why flu vaccines don’t guarantee you won’t come down with the flu. Flu viruses are constantly changing (mutating), making it possible for them to evade vaccine protections. Sometimes the strains selected for the seasonal flu vaccine are a poor match to the circulating strains.

But while flu vaccines can’t always keep you from getting the flu, people who are immunized are less likely to develop flu complications than people who aren’t.

There are several different kinds of flu vaccines, including numerous flu shot types, aimed at different age groups and catering to different needs.

Flu Shots

Ages 6 months and up:

  • Standard-Dose Shot Made with a virus grown in chicken eggs.
  • Cell-Based Shot Egg-free vaccines containing viruses grown in a culture made from mammal cells.

Ages 18 and up:

  • Recombinant Shot Synthetically created, egg-free vaccines.

Ages 65 and up:

  • High-Dose Shot Contains a bigger dose of antigen (an immunity-stimulating substance) to help create a stronger immune response.
  • Shot Made With an Adjuvant Contains an ingredient called an adjuvant that helps create a stronger immune response.
Per current recommendations, people with egg allergies can opt to receive any flu vaccine — egg-based or non-egg-based — that is appropriate for their age and health status.

Nasal Flu Vaccine

The nasal spray flu vaccine is approved for people ages 2 through 49, except for those with certain conditions. You can get this vaccine at the doctor’s office, healthcare clinic, or pharmacy, or you can purchase it online to administer yourself — no prescription needed.

The nasal spray isn’t recommended for some people with the following risk factors:

  • Those who’ve had a severe allergic reaction to a flu vaccine in the past
  • Pregnant people
  • Young people who take aspirin or a salicylate-containing medicine
  • People with weakened immune systems and those who are caregivers or close contacts of them
  • Children between ages 2 and 4 years old diagnosed with asthma or wheezing in the past 12 months
  • People who recently took antiviral medicine for the flu
  • People with a cerebrospinal fluid leak or the potential for a leak, as with a cochlear implant

The most common side effect of a flu shot is soreness, skin color changes, or swelling at the injection site.

Some people also develop other minor symptoms, including:

  • Low-grade fever
  • Headache
  • Achiness
  • Fatigue
  • Nausea
The most common side effects of the nasal spray vaccine are:

  • Fever in children 2 to 6 years old
  • Runny nose and nasal congestion in people 2 through 49 years old
  • Sore throat in adults

Flu vaccines can cause rare complications, such as:

Guillain-Barré Syndrome (GBS) Some studies have found a possible link between the flu shot and GBS, a progressive nerve disorder that can cause profound weakness for weeks or longer. Overall, studies estimate the prevalence of GBS as fewer than 1 or 2 cases per million people vaccinated.

Allergic Reaction As with any medicine, there is a remote chance that a flu vaccine can cause a serious allergic reaction (anaphylaxis), other serious injury, or even death. Anaphylaxis in children and adults triggered by flu immunization occurs in fewer than 2 cases per million vaccine doses.

Febrile Seizures A very small number of young children ages 6 months to 2 years may experience a high fever leading to seizure in the 24 hours after getting a flu shot at the same doctor visit as the pneumococcal PCV13 vaccine or the DTaP (diphtheria, tetanus, and pertussis) vaccine. While frightening for parents to watch, these seizures are over quickly and do not cause permanent injury. Studies estimate an incidence of no more than 30 febrile seizures in 100,000 children vaccinated.

Infectious disease experts recommend weighing these risks against those posed by the flu.

What About Flu Vaccines Containing Thimerosal?

Although most infectious disease specialists agree that thimerosal, a vaccine preservative, poses no health risk and has a strong safety record, the CDC’s Advisory Committee on Immunization Practices voted against recommending flu shots containing this ingredient for the 2025–2026 season.

Some members of the committee had previously voiced concerns about a link between thimerosal and autism; numerous studies have failed to find evidence for such a connection.

Prior to the committee’s decision, about 4 percent of vaccines administered in the United States contained thimerosal, but going forward all flu vaccines will be thimerosal-free.

There are a few reasons why someone might feel like they’ve gotten sick because of getting vaccinated:

Vaccine Side Effects Some people have muscle aches and a fever for a day or two after receiving a flu vaccine. This may be a side effect of your body’s production of protective antibodies.

The Two-Week Window It takes about two weeks for the flu shot to take full effect, and so if you’re exposed to the influenza virus shortly before or during that time period, you might catch the flu.

Other Illnesses Some people may experience what they believe are flu symptoms after being vaccinated because they become ill from different respiratory viruses.

Most infectious disease specialists say it’s safe and effective to get the flu shot and the COVID-19 shot at the same time. Research has shown that people who receive the shots together have no more adverse effects than people who received them one or two weeks apart, although they are more likely to experience side effects like fatigue, headache, and muscle aches.

In previous years, the CDC agreed it was safe and effective for people to get more than one vaccine at the same time.

But guidance under Health and Human Services Secretary Robert F. Kennedy Jr. appears to be changing. In a September 2025 memo, Vinay Prasad, MD, the top vaccine regulator for the U.S. Food and Drug Administration (FDA), wrote that officials “cannot affirm” the safety and efficacy of coadministering vaccines for COVID-19, flu, and other conditions, such as respiratory syncytial virus (RSV).

Dr. Prasad also said the FDA will require clinical trials before allowing pharmaceutical companies to claim that getting multiple respiratory virus vaccines at the same time is safe and effective.

If you want to get multiple shots in one visit, talk to your doctor or pharmacist.

It’s perfectly safe to get your flu shot at your local pharmacy or grocery store as well as at a doctor’s office, health or community clinic, or urgent care center.

The nasal vaccine for home use is available for order online via the FluMist Home website.

Once you locate where you will get your flu vaccine, reach out to the pharmacy or provider’s office to confirm they take your insurance, or you can call your insurance company directly.

Most recommended vaccines, including the flu vaccine, are covered by health insurance. Medicaid, Medicare Part D, and the federal Vaccines for Children program pay for all recommended vaccines for those who qualify.

If you don’t have insurance, the cost will vary depending on where you go. The shot can cost anywhere between $20 and $120, depending on the type of flu vaccine and where you get it.

  • The flu vaccine significantly reduces the risk of severe illness, making it essential for nearly everyone ages 6 months and older to get immunized annually.
  • Getting vaccinated in September or October provides the best protection during peak flu season.
  • Various flu vaccine types are available, including high-dose shots for seniors and nasal sprays for people who dislike needles or prefer to immunize themselves at home.

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