Is the Flu Vaccine a Live Virus Vaccine? 7 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). Plus, 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 seven 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 contain 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.

• mRNA vaccine: This flu vaccine doesn’t contain any flu virus either. Instead, it contains messenger ribonucleic acid (mRNA). This acts like a set of instructions for your cells. After reading the mRNA in the vaccine, your cells make a harmless protein that’s found on the surface of flu viruses. Your immune system learns how to fight real flu virus strains from this simulated protein.

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?

Each flu vaccine contains a substance that will help your immune system protect you against infection. But this substance varies, depending on which vaccine you receive:

• Inactivated flu vaccines (egg- and cell-based) contain dead flu strains.

• Live, attenuated flu vaccines contain flu strains that are alive but weakened.

• Recombinant flu vaccines contain lab-made flu proteins.

• mRNA flu vaccines contain instructions for your cells to create a protein that’s found on the surface of flu viruses.

Flu vaccines 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 2026-2027 flu season, all flu vaccines protect against the following:

• Type A (H1N1) virus

• Type A (H3N2) virus

• Type B (Victoria lineage) virus

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). For the mRNA flu vaccine, your body fights in a similar way against the proteins your cells create. 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 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 age 2

• Are between ages 2 and 4 and have recurrent (periodic) wheezing

• Are age 50 or older

• Are pregnant

• Have severe asthma or active wheezing

• 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

6. How long does a flu shot’s protection last?

The flu shot’s protection (called immunity) doesn’t last very long. After about 5 to 6 months, your level of immunity starts to fade. That’s why it’s recommended to get your flu vaccine in September or October. This helps protect you for the majority of flu season (October to May in the U.S.). But even if it’s later than October, you should still get vaccinated. It’s almost never too late to get your flu shot.

The flu shot is also custom made for each season. That’s because the flu virus mutates over time. So last year’s vaccines won’t work well for this year’s flu virus strains. That’s why it’s important to get an updated seasonal flu vaccine once a year.

7. Can you get a flu shot if you have a cold?

Yes, you can get a flu shot if you have a cold or other mild illness. Examples of other mild illnesses include:

• Sinus infections

• Ear infections

• Mild diarrhea

If you have a fever or have a moderate or severe infection, you may need to wait until you’re feeling a bit better to get vaccinated. Your healthcare team can help you determine if you’re too sick to get a flu shot.

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Written by:

Christina Aungst, PharmD, MWC

Christina Aungst, PharmD, MWC is a senior pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019.

Reviewed by:

Sheila McAdoo, PharmD

Sheila McAdoo, PharmD, is a licensed pharmacist in Virginia and New York. She has worked in the pharmacy industry for 14 years.

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