What is the flu vaccine? Things to know for the 2025 to 2026 flu season

This article is up to date as of June 27, 2025, 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.

With the 2025 to 2026 flu season fast approaching, many people are looking for answers to questions like: What is the flu vaccine? How does it work? Who should get the vaccine? When is the best time to get it?

This guide will answer these questions and more, providing useful information to help people approach the upcoming season informed and confident. Whether it’s someone’s first time or part of their annual routine, understanding the flu vaccine can offer valuable peace of mind.

In this article:

What is the flu?

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

The flu comes in four variations: A, B, C and D. Types A and B are the ones people usually get during flu season, which typically runs from October to May. Flu A is the most common, making up about 75 percent of cases.

While types A and B are similar, there are a few important differences. Flu A and B have similar symptoms, but flu A is usually more aggressive and hits harder, and it’s more common in adults. Flu B is more common in kids and usually causes a milder illness compared to Flu A, though it can be more serious for young children and older adults.

Despite the various types, many symptoms tend to overlap. Common flu symptoms include:

• Exhaustion
• Fever and chills
• Runny nose
• Sore throat

What is the flu vaccine and how does it work?

The flu vaccine is the best way for people to protect themselves and others against the flu each year. Vaccines work by training the immune system to recognize a specific virus. After vaccination, the body produces special proteins called antibodies. These antibodies act like tiny soldiers prepared to detect and fight the flu virus if it enters the body. Antibodies travel through the blood, looking for the flu virus. When these antibodies find the flu virus, they attack it and help get rid of it.

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.

When should people get the flu vaccine?

The Centers for Disease Control and Prevention (CDC) recommends everyone six months and older (with rare exceptions) get a flu vaccine every year. For most, getting vaccinated in September or October is considered a good time, but getting the vaccine later is still okay.

While that timing works well for most people, there are a few exceptions to keep in mind. Most adults should avoid getting the flu vaccine too early. Too early means getting it in July or August. Getting vaccinated that soon may cause the protection to wear off before flu season is over.

However, for pregnant individuals in their third trimester (and those who think they wouldn’t be able to get the flu vaccine later), vaccination in July and August could be considered. Getting the vaccine during the third trimester can also help protect the baby for the first few months after they’re born while they are too young to get the vaccine.

Some children need two doses of the flu vaccine to be considered fully protected. Since the second dose must be given at least four weeks after the first dose, it’s best to start early enough to finish both doses by the end of October.

Who should get a flu vaccine?

The flu vaccine is recommended for everyone 6 months and older, with rare exceptions, since anyone can get the flu. But it’s especially important for people at higher risk of serious complications, including:

• Adults 65 years and older
• Children younger than 5 years old
• People who are pregnant
• People whose immune systems are compromised, such as those with any form of cancer or who are on medications that weaken the immune system
• People with a high body mass index (BMI) of 40 kilograms per square meter or higher
• People with certain chronic conditions, such as asthma, diabetes or heart disease

Who should not get a flu vaccine?

While the flu vaccine is recommended for most people, a few groups should avoid this vaccine:

• Children younger than 6 months 
• Anyone with a severe, life-threatening allergy to a flu vaccine ingredient (other than eggs), such as gelatin or certain antibiotics
• Anyone who has had a serious allergic reaction to a previous flu vaccine

What are the benefits of the flu vaccine?

The flu vaccine offers a wide range of benefits:

• Protects against flu. Getting the vaccine lowers the chance of getting the flu and passing it to others.
• Reduces illness severity. Being vaccinated can make the flu symptoms milder if someone does get sick.
• Protects people with certain chronic conditions. The flu vaccine helps prevent serious complications and hospital stays for people with heart disease, asthma, chronic obstructive pulmonary disease (COPD), diabetes and other health issues.
• Protects pregnant people and their babies. The flu vaccine protects both the pregnant individual and their baby during pregnancy and in the newborn’s first few months.
• Protects children. Getting vaccinated reduces the risk of severe illness and flu-related death in kids.

Is the flu vaccine still recommended after having the flu?

Yes, 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.

What flu vaccines are available?

The U.S. Food and Drug Administration (FDA) has approved the following flu vaccines for use:

For children and adults:

• Afluria
• FluLaval
• Fluarix
• Flucelvax
• Flublok
• Fluzone

For adults 65 and older:

• Fluad
• Fluzone High-Dose

Health care providers can provide additional information on vaccine ingredients and age guidelines.

How is the flu vaccine given?

Health care providers choose the best spot for a vaccine based on the person’s age. Age restrictions apply.

• Babies and toddlers (under 1 to 2 years old). Vaccines are usually given in the upper thigh because the muscle there is bigger and more developed at this age compared to muscle on the upper arm.
• Anyone age 3 and older. Vaccines are given in the upper arm.

How effective is the flu vaccine?

No vaccine offers 100 percent protection. Flu vaccine effectiveness can vary from year to year, and it can depend on how closely the circulating strains match the strains covered in the vaccine itself. In general, effectiveness typically ranges from 40 to 60 percent. The flu vaccine can also help lessen symptoms and reduce the chance of complications if someone does get sick. Vaccinations have also been shown to have many other benefits, including reducing the risk of flu illnesses, hospitalization and flu-related deaths.

How long does flu vaccine protection last?

After getting a flu vaccine, it takes about two weeks for the body to build antibodies. Protection against the flu after getting vaccinated decreases over time.

How many flu vaccines should someone get?

For most people, it is recommended they only get one dose of the flu vaccine each flu season.

Flu vaccine side effects

Many people don’t experience side effects from the flu vaccine. When side effects do occur, they’re usually mild and go away on their own within a few days.

Common side effects of the vaccine may include:

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

Where can people get the flu vaccine?

Contact a health care provider for a flu vaccine or visit a CVS Pharmacy or a MinuteClinic location.

What’s in the flu vaccine?

The flu vaccine can be made by using:

• Pieces of the inactivated (killed) virus
• Synthetic pieces of the flu virus
• Weakened live virus that has been altered so it can’t cause illness

The vaccines may also contain some additional inactive ingredients such as:

• Adjuvants, which help the immune system produce a better response.
• Stabilizers, which keep the vaccine stable and effective while it’s stored and transported.
• Antibiotics, which are added in tiny amounts during manufacturing to stop bacteria from growing in the vaccine.

Changes to this season’s vaccine

For the 2025 to 2026 flu season, all flu vaccines in the U.S. will protect against three types of flu viruses: H1N1 and H3N2 (flu type A) and a Victoria virus (flu type B).

Key takeaways

The flu vaccine is a safe and effective way to protect against the flu. It helps prevent infection, can help to lessen symptoms if someone still gets sick after vaccination and lowers the risk of potential complications. Even after having the flu, the vaccine can protect against other strains.

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

This content is for informational purposes only and is not medical advice. Consult your health care provider before taking any vitamins or supplements and prior to beginning or changing any health care practices.