Is the Flu Vaccine a Live Virus Vaccine? 5 Answers to Common Flu Vaccine Questions

Fall is a season of changing temperatures, back to school, and pumpkin spice. It’s also a good time to get your annual flu vaccine. Taking this step is one of the best ways to protect yourself from influenza (the flu). What’s more, getting vaccinated helps protect those around you who are more likely to have serious flu complications, such as older adults and those with weakened immune systems.

Despite knowing how beneficial flu vaccines are, many people hesitate when it comes to getting them. In some cases, they’re concerned about the vaccination’s ingredients. For instance, many people wonder if the flu vaccine is a live virus vaccine. Others want to know about its inactive ingredients.

If this sounds like you, you're not alone. It’s normal to question what’s going into your body and how it might affect you. Below you’ll find answers to five common questions about what’s in the flu vaccine and how it works.

1. Is the injectable flu vaccine a live virus?

No. The injectable flu vaccine is not a live virus vaccine. There are a few different types of injectable flu vaccines available, none of which contains live virus strains:

• Egg-based inactivated vaccine: This is the most common type of flu vaccine. It contains dead flu virus strains. The flu virus is grown in chicken eggs before it’s inactivated (killed).

• Cell-based inactivated flu vaccine: This flu vaccine also contains dead flu virus strains. But the virus is grown inside mammal cells before being inactivated.

• Adjuvanted vaccine: This type of flu vaccine started the same way as an egg-based inactivated vaccine. But it also contains an adjuvant — a substance that helps stimulate a strong immune response.

• Recombinant vaccine: This flu vaccine doesn’t contain any flu virus (live or dead). It contains a synthetic version of one of the flu virus’ proteins. Production doesn’t involve chicken eggs or mammal cells.

What are live vaccines?

Live vaccines contain strains of the flu virus that are alive but weakened. The virus shouldn’t be strong enough to make most people sick. But because the virus is still alive, it can help your immune system respond more strongly than it would to inactivated vaccines.

Examples of live virus vaccines include:

• Measles, mumps, rubella (MMR vaccine)

• Varivax (chickenpox vaccine)

• YF-Vax (Yellow fever vaccine)

• RotaTeq (rotavirus vaccine)

2. Does the nasal spray flu vaccine contain a live virus?

Yes. FluMist (the nasal spray vaccine) is a live, attenuated flu vaccine. It contains flu virus strains that are alive but weakened. As mentioned above, it shouldn’t make most people sick. And it can provide a stronger immune response, potentially offering greater protection against the flu.

Good to know: FluMist is an egg-based flu vaccine. Similar to inactivated, egg-based vaccines, the flu virus is grown in chicken eggs during production.

3. What is the flu vaccine made of?

The flu vaccine contains flu strains (or synthetic flu proteins, for recombinant vaccines). They are created based on what scientists believe will be the most prevalent strains during the upcoming flu season. Their composition changes every year to offer the best protection.

The FDA requires that all flu vaccines are standardized. For the 2024-2025 flu season, all flu vaccines protect against the following:

• Type A (H1N1) virus

• Type A (H3N2) virus

• Type B (Victoria lineage) virus

EXPERT PICKS: WHAT TO READ NEXT

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Flu vaccines also include a few inactive ingredients. These typically help stabilize the vaccine or are used during its production. The specific inactive ingredients vary between flu vaccines. They may include:

• Squalene: This is a substance found naturally in skin oil. It’s the adjuvant that’s included in adjuvanted flu vaccines.

• Stabilizers: These extend flu vaccines’ shelf lives. They include substances that are found naturally in the environment, such as sugars and amino acids (protein building blocks).

• Thimerosal: This is a preservative that helps prevent germs, such as bacteria and fungi, from growing inside flu vaccine vials. Thimerosal is only included in multiple-dose vials. Most flu vaccines are single-dose vials or syringes and do not contain it.

• Egg protein: This is found in egg-based flu vaccines because of how they’re made. A tiny amount of egg protein may be present. But it’s not typically enough to be a problem if you have an egg allergy.

• Antibiotics: These are included to prevent bacterial contamination during production of the flu vaccine. Only trace amounts remain in the vaccine when you receive it. And they are antibiotics that are very unlikely to cause allergic reactions.

• Formaldehyde: This is included in some inactivated flu vaccines to kill the virus. Only trace amounts are present in the vaccines. There isn’t enough formaldehyde in the flu vaccine to harm you. In fact, a greater amount of formaldehyde is found naturally in your body.

4. How does the flu vaccine work?

The flu vaccine works similarly to other vaccines. It teaches your immune system how to fight the flu virus.

When you receive the flu vaccine, your immune system sees it as an invader. It fights against the virus in the vaccine (or synthetic proteins in the recombinant vaccine). This is why you sometimes feel flu-like symptoms after getting it.

After responding to the vaccine, your immune system remembers how to fight against the flu. So if you come into contact with the flu, you’re less likely to get sick with it. And even if you do get sick, you’re less likely to develop serious symptoms or complications.

5. Who shouldn’t get a live virus flu vaccine?

FluMist is FDA-approved for people ages 2 to 49. But it isn’t recommended for everyone in this age range. Some people may have a greater risk of certain side effects or complications after receiving it.

People who shouldn’t get the nasal spray flu vaccine include those who:

• Are under 2 years old

• Are between 2 and 4 years old and have asthma

• Are 50 years or older

• Are pregnant

• Have a weakened immune system

• Take medications that weaken the immune system, such as prednisone

• Will have close contact with a person who has a severely weakened immune system within 7 days after receiving FluMist

• Have cochlear implants (implantable devices that can help provide sound for certain people who are Deaf or have severe hearing difficulties)

• Have previously experienced a severe allergic reaction to a flu vaccine

• Have recently taken flu antiviral medications, such as Tamiflu (oseltamivir) — flu antivirals make FluMist less effective

Who shouldn’t get the inactivated flu vaccine?

Almost everyone can receive an inactivated flu vaccine. Most of these vaccines are FDA-approved for people ages 6 months and older. And it’s recommended that everyone who can get vaccinated does so once a year in the fall.

Infants under 6 months old are the only group of people who cannot get any type of flu vaccine. But there are other people who should ask a healthcare professional first about whether it’s safe for them to get vaccinated. They may need to look for a specific type of flu vaccine. And in rare cases, some people might need to avoid them altogether.

Ask a healthcare professional about whether you can get a flu vaccine if you:

• Have had a life-threatening allergic reaction to any vaccine (flu or otherwise)

• Have had Guillain-Barré syndrome (an autoimmune disorder that affects the nerves)

• Are feeling sick or have symptoms of an illness, such as a fever or cough

Why trust our experts?

Written by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Jennifer Gershman, PharmD, CPh, PACS

Jennifer Gershman, PharmD, is a licensed pharmacist in Florida. She has worked in the pharmacy industry for more than 15 years and is currently a medical writer.

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