What to Know About Flu Vaccine Effectiveness – Verywell Health

While flu vaccine effectiveness varies year-to-year, research shows that flu vaccines are typically between 40% and 60% effective during years when the most prevalent flu strains match the strains in the vaccine. This means the vaccine reduces your risk of catching the flu by 40% to 60%.

The vaccine also reduces the likelihood of severe illness, hospitalization, and death. Because of this, the Centers for Disease Control and Prevention (CDC) recommends that everyone ages 6 months and over gets the flu vaccine (with very rare exceptions).

There are nine different flu vaccines available for the 20232024 flu season. All of them protect against the same four strains of flu. Heres what you should know about flu vaccine effectiveness and types of flu vaccines.

Verywell / Theresa Chiechi

Each year, the flu vaccine is designed to protect against the flu strains that scientists believe will be most common. However, the effectiveness of the flu vaccine depends on which flu strains are most prevalent and how they compare to the strains that the vaccine protects against.

Because of this, flu vaccine effectiveness varies from year to year. Scientists dont yet have final estimates for the effectiveness of the flu vaccine for the 20222023 season, but preliminary data show a range of 39%-44% effectiveness in adults.

The CDC tracks seasonal flu vaccine effectiveness each year. Over the past 17 years, the highest effectiveness was in the 2010-2011 season, when it was 60% effective.

Here are the effectiveness rates over the past five seasons for which data are available:

During the 20202021 flu season, the CDC didnt estimate the effectiveness of the vaccine because transmission of the flu was historically low, likely due to COVID-19 precautions that also protect against the flu.

The flu vaccine (flu shot or nasal spray vaccine) significantly reduces the risk of contracting the flu. Consider the 20192020 season: People who had the vaccine were 39% less likely to get the flu than those who did not.

In addition to preventing illness, the flu vaccine also reduces the risk of hospitalization and death. Heres what researchers have found about the flu vaccine:

In addition to protecting you, getting the flu vaccine can keep you from contracting the flu and passing it to others, including infants and the elderly, who are at higher risks for complications.

Pregnant people who get the vaccine help protect their baby from the flu (passing on the protective antibodies developed by the vaccine), which can be valuable during the first six months of life when a child is not able to be vaccinated.

There are a number of factors that influence how effective the flu vaccine is every year. The most important is strain matchingwhether the strains that the vaccine protects against match the most widely circulating flu strains during a given season.

In addition to the construction of the vaccine, there are more personal factors that influence vaccine effectiveness.

To decide which strains are covered by the flu vaccine, data on flu infections are collected from around the globe. Using that, the World Health Organization (WHO) meets twice a year to decide which strains to focus on in the vaccines.

For the Northern Hemisphere, the WHO makes a recommendation in February. In the United States, the Food and Drug Administration (FDA) has the final say in which strains are included in the vaccine.

The decision about which strains to include is based on projections that are made using past data. This gives time to manufacture the vaccine.

It takes two weeks for the flu vaccine to become optimally effective. Because of that, the CDC recommends that all people get the flu vaccine during September or October, before flu infections become widespread.

Getting the vaccine too late can leave you exposed to early infection from the flu. On the other hand, vaccine protection begins to wane after several months. Adults ages 65 and older are generally not vaccinated early (July or August) due to this.

The CDC recommends the vaccine (even later in the season) for people who didn't get vaccinated in by October since flu can spread throughout the spring.

CDC data show that within a given year, the protection that the flu vaccine offers can vary based on age due to immune changes over time. Theres no way to predict which age groups the flu vaccine will be most or least effective for in a given season.

The CDC recommends that people age 65 and older receive a higher-dose or adjuvanted flu vaccine.

Vaccines rely on a person's immune system responding to the vaccine by producing antibodies, which are proteins that have specific targets, in this case on the influenza virus.

If a person has an impaired immune system due to a health condition, they may not mount the desired immune response, reducing the vaccine's effectiveness. There are a wide variety of health conditions that can impair your immune system response.

This is one reason that everyone should be vaccinated. By having less risk of getting and spreading the flu, they protect those who have impaired immunity and, therefore, can't benefit as much from vaccinating themselves.

There are nine types of flu vaccines (shots and nasal spray) available for the 2022-2023 season. All nine protect against the same four strains of flu. Because they protect against four they are called quadrivalent vaccines.

The CDC doesnt recommend one type of vaccine over the others. However, some people, including people under the age of 2, over the age of 65, who have allergies, or are pregnant, have special considerations and should talk to their doctor about which vaccine is best.

Some studies indicate that a higher-dose vaccine or an adjuvanted flu vaccine (one with an additional substance called an adjuvant that enhances the body's immune response to an antigen) creates a stronger immune response) produce a stronger immune response and are therefore more effective for this population.

The CDC recommends people age 65 and older receivea higher-dose vaccine or an adjuvanted flu vaccine (one with an additional substance called an adjuvant that enhances the body's immune response to an antigen). Three vaccines are specifically recommended for this population:

According to the CDC, people who have severe allergies to an ingredient in the flu vaccine or who have had a severe reaction to the flu vaccine should not get a flu shot.

Most flu vaccines are made using eggs or egg protein, but the CDC states that people with egg allergies can get any flu vaccine, regardless of the severity of their allergy. The CDC previously had recommended that people with egg allergies should get their flu shots in an inpatient or outpatient setting. For those interested in an egg-free flu shot, the two egg-free vaccine options are:

Pregnant people can get any flu vaccine except for FluMist, which contains a live virus.

FluMist Quadrivalent is a vaccine administered via a nasal spray. It is approved for people ages 2 through 49. However, its the only vaccine that contains a live, weakened virus, and it should not be used by pregnant or immunocompromised people. Talk to your healthcare provider about whether FluMist is safe for you.

There are five flu vaccines approved for babies 6 months and older. They are:

The flu vaccine needs two weeks to become fully effective, and protection is thought to last for at least six months. But a person's antibody levels in response to the vaccine can decrease over time, and different flu strains may be circulating.

Because of that and because each year the vaccine is tailored to the most concerning flu variants, people should get a flu vaccine annually.

Side effects of the flu vaccine are usually mild and go away without treatment in a few days. Common side effects include:

Rarely, allergic reactions occur, often within minutes of the vaccine being administered. If you experience swelling, racing heart or trouble breathing, seek medical attention immediately. Extremely rarely (no more than one or two cases per million people who receive the flu vaccine) a person may develop Guillain-Barr syndrome, an autoimmune disease.

The flu vaccine can prevent illness, hospitalization, and death. The CDC recommends that everybody aged 6 months and older get the vaccine every year (with very rare exceptions). The effectiveness of the vaccine varies since the vaccine only protects against certain strains of flu. Over the past five years, the effectiveness of the flu vaccine has ranged from 29%40%.

Deciding whether to vaccinate can be a big decision. Although the flu is a common illness, it can be deadly, particularly for people over the age of 65. The flu vaccine isnt 100% effective, but it does significantly reduce the risk of illness, hospitalization, and death.

If you have questions about the vaccine, talk to your doctor about whether it is right for you or your children.

The flu vaccine first became available in the 1930s, and it became widely available in 1945.

Flu vaccine effectiveness varies from year to year. It depends on how well the strains in the vaccine match the strains that are most prevalent in a given year.

Yes, the CDC says that the flu vaccine and COVID-19 vaccine, including boosters, can be administered at the same time.

The flu shot is made with either killed or weakened flu virus. The shots also contain inactive ingredients, including preservatives.

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What to Know About Flu Vaccine Effectiveness - Verywell Health