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Oct 31, 2024

Flu Shot Ingredients: Safety, Benefits, and Side Effects

If you worry about flu shot ingredients, you should know that they have a decades-long history of safety. With only a few exceptions, such as a rare allergy to one of the ingredients, flu vaccines are

If you worry about flu shot ingredients, you should know that they have a decades-long history of safety. With only a few exceptions, such as a rare allergy to one of the ingredients, flu vaccines are safe for everyone ages 6 months and older.

Most importantly, getting a flu shot every year protects you from severe flu-related complications like ear infections, pneumonia, and dangerous heart inflammation. Flu vaccine ingredients change every year, depending on the flu virus strains that are expected to be circulating. Otherwise, they typically contain several basic ingredients.

Verywell / Theresa Chiechi

The shot for the 2024-25 flu season is a trivalent vaccine. That means it protects against three different flu viruses: two influenza A viruses and one influenza B virus. In some previous years it was trivalent, while it was quadrivalent (covering four different viruses) in others.

Flu shots vary in ingredients, manufacturing method, brand, and delivery. These are the ingredients typically found in most flu vaccines.

Egg-based flu vaccines are produced by growing inactivated versions of the flu virus in fertilized chicken eggs. The virus replicates in the egg, then it's extracted and used in vaccines. This is the most common flu shot manufacturing process, and it’s been used safely for over 70 years.

Examples of standard-dose flu vaccines made with egg-based manufacturing methods include:

Egg proteins are a common flu shot ingredient, but there are now two ways of manufacturing flu vaccines that eliminate exposure to eggs:

There are currently two egg-free flu vaccines available in the United States:

Some versions of the flu vaccine contain adjuvants, which are varying ingredients that trigger a stronger immune response. These vaccines are recommended for adults over the age of 65 and aren't suitable for everyone.

One adjuvanted flu vaccine, FLUAD, contains a non-aluminum adjuvant (MF59) and is produced using an egg-based process.

Antibiotics, such as neomycin, are added to some flu vaccines to prevent bacterial contamination during the manufacturing and storage process. Antibiotics that commonly cause allergic reactions, such as penicillin, aren’t used by vaccine manufacturers.

A small amount of thimerosal is added to multi-dose vials of the flu vaccine to prevent contamination by bacteria. Multi-dose vials are used to give flu shots to several people.

Many people are concerned about thimerosal. However, most flu vaccines are produced in single-dose vials and don't contain this preservative. Since a few companies still produce multi-dose vials, talk with your healthcare provider to learn about the flu shot ingredients in the vaccines they offer.

Stabilizers, such as gelatin or sugar (sucrose), help to protect vaccines from damage by heat or light after they’ve been manufactured.

Inactivating ingredients are used to kill the virus (producing the inactivated viruses used to make the vaccine). These ingredients may also be added during processing to eliminate toxins.

One inactivating ingredient, formaldehyde, is removed after the vaccine is produced but trace amounts may still remain in certain flu shots. Not all vaccines use formaldehyde, so talk with your healthcare provider to learn if your flu shot has this ingredient.

Formaldehyde is produced naturally in the body, where it’s used to build proteins. It’s also present in the environment. However, formaldehyde in large amounts that far exceed the traces found in vaccines can cause cancer.

According to the FDA, the amount of formaldehyde in the average newborn’s body at just 6 to 8 pounds is already 50 to 70 times higher than the highest possible amount of formaldehyde in any vaccine.

There are two main versions of the flu shot, both of which use your body’s natural defenses to trigger an immune response and create the antibodies that fight the flu virus. The two types include:

You can't get the flu from either type of vaccine.

There are three ways the flu shot can be delivered:

All flu vaccines on the market meet the safety and efficacy requirements set by the Food and Drug Administration (FDA).

If you’re worried about ingredients that are controversial or might cause adverse reactions, you need to know that flu vaccines in the United States do not contain:

Flu vaccines are not in packaging that contains latex, so they’re safe for people with latex allergies.

Flu viruses change frequently, so new flu shots are produced every year to contain the dominant viruses for that season. According to the Centers for Disease Control and Prevention (CDC), flu shot composition is decided each year with the help of over 144 influenza centers in over 114 countries.

Laboratories at each center collect influenza surveillance data throughout the year and send virus samples to the World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza. The FDA makes the final determination on which strains to target in the U.S.

By exposing you to a dead or weakened version of the flu virus, the flu shot causes your body to develop antibodies to the virus about two weeks after vaccination.

Antibodies neutralize the virus and activate immune cells that destroy it, protecting you from getting the flu. They can also protect you from developing severe influenza complications such as pneumonia, sinus infections, and ear infections if you do get sick.

The effectiveness of the flu shot can vary based on your age, overall health, and how well the vaccine matches the flu viruses that are circulating in your area.

Still, the vaccine can reduce your risk of having to seek medical attention due to the flu by up to 40 percent to 60%.

The CDC recommends that all people ages 6 months and older get the flu shot every year, with few exceptions. Flu shots are generally considered safe and effective, but may cause temporary side effects or allergic reactions.

The most common flu shot side effects include:

More rarely, the flu shot (like other vaccines) can cause dizziness or fainting. Some studies have shown extremely rare cases of Guillain-Barré syndrome (GBS) after the flu shot, while others have shown no association. The nasal spray has not been associated with any cases of GBS.

Additional side effects from the nasal spray flu vaccine can include:

Allergic reactions to flu shots are rare, but can occur in response to one of the ingredients. After getting any vaccine, you should watch for signs of a severe allergic reaction. These could include:

Seek immediate medical attention if you see any of these signs or symptoms a few minutes or hours after getting the flu shot, as they could be fatal.

If you have a severe allergic reaction to the flu shot, you shouldn't get vaccinated.

You can get a flu shot even if you have an egg allergy. According to the CDC, people with a history of egg allergy can safely get any flu vaccine regardless of the severity of their egg allergy. However, all flu vaccines should be given in a facility equipped to recognize and treat allergic reactions to other ingredients.

Talk with your healthcare provider if you're concerned about an egg allergy. They can determine if a routine flu shot is safe for you or recommend a non-egg-based vaccine.

Most children ages 6 months and older should get an annual flu vaccine. Side effects in children are typically as mild as those in adults.

The nasal spray flu vaccine is approved for most children and adults between the ages of 2 and 49. However, some children shouldn't get the nasal spray flu vaccine, including:

Adults ages 65 and up should get an annual flu shot. They shouldn't get the nasal spray flu vaccine.

The regular flu shot is safe and effective for older adults. However, vaccines don’t always prompt a strong immune response among people in this age group. There are two vaccines designed specifically for those ages 65 and older:

The flu shot is one of the best ways to protect yourself from the seasonal flu, but there are other steps you can take to stay as healthy as possible. Learn when to get the flu shot and other flu prevention tips.

The flu vaccine needs two weeks to build up antibodies and protect you from the virus. That means most people should get their vaccination at the start of the flu season (September and October).

If you aren’t able to get vaccinated by the end of October, don’t skip it. Flu season peaks in February but runs through May, so you can still protect yourself.

The CDC recommends early vaccination (usually in July or August) for children as well as for people in the third trimester of pregnancy. Adults, especially those aged 65 and older, should avoid early vaccination because protection from the vaccine wanes over time.

In addition to the seasonal flu shot, these preventive healthy habits can help protect you and your loved ones from the flu.

The flu vaccine is safe and effective for most people in protecting against the flu virus. It’s recommended that all people ages 6 months and older get a flu shot every year, ideally by October.

Some ingredients in the seasonal flu vaccine vary from year to year based on the flu virus strains expected to cause illness. Other ingredients, such as preservatives, stabilizers, adjuvants, antibiotics, and inactivating ingredients, are common in vaccines and have been extensively tested for safety and effectiveness.

The flu shot has been used safely in the U.S. since the 1940s.

It can protect you from catching, spreading, or getting severe complications from the seasonal influenza virus. Talk with your healthcare provider if you have questions about flu shot ingredients or which version of the flu shot you should get.

Centers for Disease Control and Prevention. Seasonal flu vaccine basics.

CDC Vaccines and Immunizations. Inactivated influenza vaccine information statement.

Centers for Disease Control and Prevention. Different types of flu vaccines.

Centers for Disease Control and Prevention. How influenza (flu) vaccines are made.

Centers for Disease Control and Prevention. Adjuvanted flu vaccine.

FDA, Fluad quadrivalent

Centers for Disease Control and Prevention. What's in vaccines?

Centers for Disease Control and Prevention. Vaccine basics.

Children’s Hospital of Philadelphia. Flu vaccine: What’s in the vial?

Children’s Hospital of Philadelphia. Vaccine ingredients: Formaldehyde

U.S. Food and Drug Administration. Common ingredients in U.S. licensed vaccines.

Centers for Disease Control and Prevention. Live Attenuated Influenza Vaccine [LAIV] (The nasal spray flu vaccine).

Centers for Disease Control and Prevention. Selecting viruses for the seasonal influenza vaccine.

Centers for Disease Control and Prevention. Benefits of the flu vaccine.

Centers for Disease Control and Prevention. Flu vaccine safety.

Centers for Disease Control and Prevention. Key facts about seasonal flu vaccine.

CDC Vaccinations and Immunizations: Live intranasal influenza vaccine information statement

Grohskopf LA, Sokolow LZ, Broder KR, et al. Prevention and control of seasonal influenza with vaccines. MMWR Recomm Rep. 2016;65(5):1-54. doi:10.15585/mmwr.rr6505a1

Centers for Disease Control and Prevention. Flu vaccine and people with egg allergies.

Centers for Disease Control and Prevention. Flu and Children.

National Library of Medicine: MedlinePlus. Salicylate level.

Centers for Disease Control and Prevention. Flu & people 65 years and older.

Centers for Disease Control and Prevention. Healthy habits to help protect against flu.

Centers for Disease Control and Prevention. Influenza historic timeline.

By Laura DorwartDr. Dorwart has a Ph.D. from UC San Diego and is a health journalist interested in mental health, pregnancy, and disability rights.