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What is the flu vaccine?

What to know about this season’s flu vaccine and how it works.

Updated: August 13, 2026 | 14 minutes to read

Written by: Max Schochet

A person receives an adhesive bandage after getting a flu shot.

This article is up to date as of June 17, 2026, and based on vaccine guidance provided by the U.S. Centers for Disease Control and Prevention (CDC). Individual states may adopt their own vaccine policies and recommendations based on local public health assessments and regulatory frameworks. For the most up-to-date information, consult your state or local health department or your health care provider.

During flu season, many people have questions about the flu vaccine. These often include what the vaccine it is, how it works, who should get it, when to get it and which flu strains are circulating.

Understanding the basics about the flu vaccine can help people make informed decisions in protecting their health. This guide will provide helpful information for anyone looking to learn more about the flu vaccine, whether they’re getting vaccinated for the first time or as part of a yearly routine.

In this article:

What is the flu?

Influenza (flu) is a common, highly contagious respiratory illness that affects the nose and throat, and sometimes the lungs.

There are four types of flu viruses: A, B, C and D. Of these, types A and B are the main viruses that spread in humans during flu season.

Flu A in particular is responsible for flu pandemics, which are global outbreaks. It has two subtypes that commonly circulate in people: A(H1N1) and A(H3N2).

Flu B viruses don’t have subtypes. Instead, they are divided into two lineages: B/Victoria and B/Yamagata, named after the locations where they were first identified. The B/Victoria lineage still circulates in the U.S. during flu season. The B/Yamagata lineage has not been detected in the U.S. since March 2020.

In contrast, flu C usually causes mild illness but isn’t linked to outbreaks in people. Flu D mainly affects cattle and can spread to other animals, but it’s not known to cause illness in humans.

Flu signs and symptoms

Flu symptoms often appear suddenly, usually about two days after exposure. However, it can take anywhere from one to four days for symptoms to appear.

People with the flu may experience some or all of the following symptoms:

  • Cough
  • Fatigue (feeling very tired)
  • Fever or chills (not everyone has a fever)
  • Headaches
  • Muscle or body aches
  • Runny or stuffy nose
  • Sore throat

Some people, especially children, may also experience vomiting and diarrhea.

When is flu season?

In the U.S., flu season usually happens in the fall and winter. Even though people can get the flu any time of year, cases typically peak between December and February.

What determines how severe a flu season will be?

The severity of a flu season can depend on several factors, which may include:

  • How many people are vaccinated
  • How well the vaccine works
  • Which flu viruses are circulating, and in what proportion

What is the flu vaccine?

The flu vaccine is a seasonal vaccine that helps protect against the influenza viruses most likely to spread each year.

How does the flu vaccine work?

The flu vaccine helps the body produce antibodies that protect against the flu viruses most likely to circulate each season, which may include influenza A(H1N1), A(H3N2) and influenza B/Victoria.

Help protect yourself from the flu this season. Schedule a flu shot at a CVS Pharmacy location or speak with a health care provider today.

What’s new for this season’s flu vaccine?

Flu viruses can change over time through small genetic mutations. Because of this, the flu vaccine is updated each year to match the strains most likely to spread in the U.S.

Since 2024, all flu vaccines used in the U.S. have been trivalent, meaning they protect against three virus types: influenza A(H1N1), A(H3N2) and influenza B/Victoria.

For the 2026 to 2027 season, all three components of the vaccine will be updated, including changes to better target the influenza A(H3N2) strain that spread widely during the previous 2025–2026 season.

The B/Yamagata lineage is not included because it has not been detected through global surveillance since March 2020 and is considered a low risk.

Who should get a flu vaccine?

Everyone 6 months and older should get a flu vaccine, with few exceptions.

Vaccination is especially important for people at higher risk of complications from the flu. This includes adults 65 and older, children younger than 2 and pregnant people. People with certain health conditions, such as asthma, coronary artery disease or obesity, are also at higher risk of flu complications.

Anyone who is unsure whether they should get the flu vaccine should contact a health care provider.

Flu vaccine dosage recommendations

It is recommended that everyone older than 6 months receive a flu vaccination every flu season. Most people only need one dose per season. Some children, however, may need two doses in the same season. These include:

  • Children ages 6 months to 8 years who’ve never had a flu vaccine or whose vaccine history is unknown.
  • Children ages 6 months to 8 years who haven’t received at least two prior doses of flu vaccine.

Who should NOT get a flu vaccine?

While the flu vaccine is recommended for most people, a few groups should not get it:

  • Children younger than 6 months
  • People with a severe allergy to any ingredient in the vaccine (except egg proteins), such as gelatin or certain antibiotics
  • People who have had a severe allergic reaction to a flu vaccine in the past

It’s recommended that people talk to a health care provider to decide if the flu vaccine is right for them.

[On-screen text: On The Beat by CVS]

[CVS pharmacists demystify vaccines.]

Edwin, speaking: What’s your thoughts on vaccines?

Alexandra, speaking: Where to begin?

Edwin, speaking: Hmmm…

[On-screen text: How do vaccines work?]

[Lower Third 1: Alexandra CVS Pharmacist 8 years]

[Lower Third 2: Edwin CVS Pharmacist 16 years]

[Bubble: Vaccines prepare your body for various viruses.]

Alexandra, speaking: Vaccines work by eliciting a response in the body by your immune system.  It tells your body that we need to be prepared by having some of that immunity ahead of time.

Edwin, speaking: The good thing is, if you have any questions or concerns, you can consult with your pharmacist.

[On-screen text: When should I get vaccinated?]

[Bubble: There are many reasons to consider getting vaccinated.]

Edwin, speaking: The flu shot is an annual shot, but we also have other reasons for people to come in and get additional vaccines. Changes in the family dynamics.

Alexandra, speaking: People who are pregnant or might be welcoming a baby into the family.

Alexandra, speaking: The shingles shot. You get one dose, and then you get the second dose 2 to 6 months after your first dose.

Edwin, speaking: The two-dose series makes it highly effective.

Edwin, speaking: Travel vaccines.

Alexandra, speaking: Check with your CVS pharmacist, they can help you review the guidelines and let you know which vaccines you need for which country you’re going to.

[On-screen text: Why is the flu shot so important? And what should I know going in?]

[Bubble: The flu virus can change every year, so it’s important to get vaccinated annually.]

Alexandra, speaking: It's very important to get your flu shot every year because every year it can change a little bit. And you can also lose your immunity as well. That's why it's important to get vaccinated every fall.

Edwin, speaking: I think a lot of times we don't realize that we’ve also got to protect ourselves but also protect others that are around us.

Alexandra, speaking: Right. If we care about our friends and our family around us, making sure that we get vaccinated, it can help protect them, too.

Edwin, speaking: Absolutely.

[What should I know about side effects?]

[Bubble: Flu shot side effects include fatigue and soreness or redness at the injection site.]

Edwin, speaking: After you get a vaccine it can make you feel fatigued. Might have some time at the injection site area, a little redness.

Alexandra, speaking: They basically wake your body up and say, hey, we want you to be prepared in case you were to come in contact with this virus.

[On-screen text: How does CVS help my family stay up-to-date?]

[Bubble: You CVS pharmacist can help you manage all the details of your vaccine schedule.]

Alexandra, speaking: I think the last thing on a lot of our minds are, “Am I up to date on all of my recommended immunizations?” Sometimes the recommendations are changing so often, it's hard to keep track, but you know what you can do? Contact your CVS pharmacist and we can make sure that we're up-to-date on all the latest updates to those guidelines and make sure that you're protected.

[On-screen text: Are vaccines covered by insurance?]

[Bubble: Most insurance include your vaccines as a covered benefit.]

[Bubble: If a vaccination is not covered by your insurance, we can help you find other ways to save.]

Alexandra, speaking: For most insurances, vaccines are considered preventative care, and it's a covered benefit under your insurance. And usually there's no copay at all to get your vaccines at the pharmacy. But it’s important to check insurance coverage for questions.

Edwin, speaking: In some cases where insurance does not cover, we do have other options. We'd like to take the time out to be able to help save you money and save you time.

[On-screen text: Is it easy to get a vaccination at CVS?]

[Bubble: Getting your vaccination at CVS is a really streamlined, quick and efficient process.]

Alexandra, speaking: I think CVS makes it so easy to get your vaccine.

Edwin, speaking: I just scheduled my appointment the other day.

Alexandra, speaking: Yeah. Did you do it online?

Edwin, speaking: I did it on the app.

Alexandra, speaking: It's so easy. It's great when you come to the pharmacy, it makes it a really streamlined, quick, efficient process to get your vaccine.

Edwin, speaking: But keep in mind, though, even if you don't have access to technology or you don't have time, walk-ins are always welcome.

Alexandra, speaking: And we give you a nice private area to give that vaccine.

Edwin, speaking: Privacy is important.

[On-screen text: How do you help people who are nervous?]

[Bubble: If you’re nervous about getting a shot, your pharmacist can help.]

[Bubble: STICKERS!]

Edwin, speaking: Vaccines can be a stressful time, and that's the great thing about coming to see your pharmacist, because that allows us to be able to build trust with you, but also allow you to be able to relax, talk to you and calm you through the process. I mean, sometimes when the kids come in, they’re not happy about getting a vaccine.

Alexandra, speaking: Right. They get so worked up and so scared.

Edwin, speaking: It gives me a chance to be able to spend some time with them, allow them to be able to build trust with me, and then the fun part at the end? It’s that sticker.

Alexandra, speaking: The stickers.

Edwin, speaking: Oh man.

Alexandra, speaking: Stickers…I think instead of, you know, maybe a pediatrician's office where only the kids can get vaccinated or only adults, you know, we're able to help the whole family. So, I think it does help a lot when a kid can see their mom or dad getting a vaccine. Most of the time after I give a vaccine, I hear, “Are you done already?” 

Alexandra, speaking: We make it pain-free, as pain-free as we can.

Alexandra, speaking: If you found this information helpful, please like and subscribe for more information from helpful CVS pharmacists.

When to get the flu vaccine

September and October are the recommend times for people to get the flu vaccine. Ideally, vaccination should take place by the end of October. However, some groups may need slightly different timing:

  • Most adults, especially those 65 and older and those who are pregnant, may benefit from waiting until September or October, since protection can decrease over time
  • Vaccination earlier in the season (July or August) is appropriate if it’s too difficult to get vaccinated later.
  • Some children need two doses, so the first should be given as soon as the vaccine is available.
  • Vaccination during the third trimester (July or August) can help protect newborns after birth.
Health care provider consults with a patient about getting vaccinated.

What are the benefits of the flu vaccine?

There are several reasons people should consider getting a flu vaccine each year. It:

  • Helps prevent the flu
  • Helps protect children from developing a more severe, possibly life-threatening flu
  • Helps protect others, especially those at higher risk for flu infection (e.g., young children, older adults and people with certain chronic health conditions)
  • May reduce symptom severity if illness occurs

What flu vaccines are available?

There are two types of flu vaccines used in the United States: injectable vaccines (shots) and a nasal spray vaccine.

Injectable vaccines

There are several approved flu shots for children and adults. While they may be made using different methods or formulas, they all work toward the same goal of helping protect against the flu.

People should talk to a health care provider to find out which flu vaccine is right for them.

How are flu vaccines given?

Flu shots are usually given in the upper arm (deltoid muscle) for anyone over the age of 3. For infants and younger children (under age 3), the shot is typically given in the thigh. The nasal flu vaccine is given as a spray in the nose to eligible people who are ages 2 through 49.

How effective is the flu vaccine?

No vaccine provides 100 percent protection. The flu shot’s effectiveness can vary depending on how well it matches the viruses circulating that season.

This effectiveness is sometimes measured by how much it helps reduce the risk of health care visits and hospitalization. In some seasons, it may be lower than in others. Even so, the vaccine still helps protect against serious illness. The flu vaccine provided the following benefits in the 2025–2026 flu season:

Children and teens:

  • About 38 percent to 41 percent protection against flu-related health care visits
  • About 41 percent protection against flu-related hospitalization

Adults:

  • About 22 percent to 34 percent protection against flu-related health care visits
  • About 30 percent protection against flu-related hospitalization

After getting a flu vaccine, it takes about two weeks for the body to build antibodies. Protection can also decrease over time.

 

A health care provider helps a customer compare over-the-counter products.

Flu vaccine side effects

The flu shot doesn’t cause the flu. However, some people may experience mild and short-lived side effects that can feel similar to flu symptoms.

These side effects may differ depending on whether someone gets a flu shot or the nasal spray vaccine.

Flu shot

Possible side effects may include:

  • Fatigue
  • Fever
  • Headache
  • Muscle aches
  • Nausea
  • Soreness, redness or swelling at injection site

Nasal spray

Side effects of the nasal spray vaccine can vary by age.

Possible side effects in children:

  • Headache
  • Low-grade fever
  • Muscle aches
  • Runny nose
  • Vomiting
  • Wheezing

Possible side effects in adults:

  • Cough
  • Headache
  • Runny nose
  • Sore throat

If side effects occur, they usually start soon after vaccination and go away on their own. In rare cases, a flu shot can cause fainting, as can other injections.

Serious side effects

There’s a small increased risk of Guillain-Barré Syndrome (GBS), a rare neurological condition, after flu vaccination. As with any medication, there’s also a very small chance of a severe allergic reaction or other serious complications.

What is in the flu vaccine and how is it made?

Flu vaccines are made using three main methods:

  • Egg-based (most common): The virus is grown in chicken eggs
  • Cell-based: The virus is grown in lab-grown cells
  • Recombinant: Only a protein from the virus is produced

With egg-based and cell-based vaccines, the virus is grown and then killed (for flu shots) or weakened (for the nasal spray). Recombinant vaccines don’t use the full virus.

Every ingredient in a vaccine serves a purpose. In addition to antigens, which help activate the immune system to fight infection, vaccines contain other ingredients that help keep them safe and effective. These ingredients may include:

  • Adjuvants: Ingredients that help boost the body’s immune response to the disease it is being vaccinated against
  • Preservatives: Ingredients that help prevent the growth of bacteria or fungi that might be introduced into a vaccine during its use
  • Stabilizers: Ingredients that help keep a vaccine effective after manufacturing

Key takeaways

The flu vaccine helps protect against the flu by helping reduce the risk of illness, lessening symptom severity if infection still happens and helping prevent complications. It’s updated each year to match the strains most likely to spread. While effectiveness can vary, it remains an important tool for reducing health care visits and hospitalizations. Because flu viruses change and protection fades over time, yearly vaccination is recommended, even for people who have already had the flu or received the vaccine in previous years.

Frequently asked questions (FAQs)

People can get a flu vaccine at the same time as other vaccines. There’s no required waiting period between them. For example, flu and COVID-19 vaccines are often given during the same visit if a person is eligible.

People can get the flu more than once in a season if different strains circulate. Getting sick with one strain won’t protect someone from another strain, and the vaccine may not cover every strain. That’s why getting vaccinated still matters, even for people who have already had the flu.

The flu vaccine is still needed even after someone has had the flu. That’s because there are multiple flu strains, and getting sick once doesn’t protect against all the strains. The flu vaccine helps protect against several strains each season.

Individuals with an egg allergy can get any age-appropriate egg-based or non-egg-based flu vaccine. Serious reactions are very rare, and egg-free versions are available if desired. Anyone concerned should talk to their health care provider to learn if the flu vaccine is safe and right for them.

When someone with the flu coughs or sneezes, droplets with the virus can spread to people nearby. It can also be spread by hands contaminated with the virus.

This content is for informational purposes only and is not intended to replace professional medical advice, diagnosis or treatment. Consult your health care provider if you have any questions about medications, vitamins or supplements you may be considering or changes to your wellness or health care routines.

Vaccine availability varies by state based on regulations. Age restrictions apply. Available when a certified immunizer is on duty.

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