What’s Really in a Flu Shot?

By Olivia Kinney, PharmD

As a pharmacist, I often answer questions about flu shots. Should I get a flu shot? The answer is yes! Can you get the flu from a flu shot? No! What’s really in there? The truth is, the shot is only made up of essential ingredients, including:

Four inactivated flu viruses:

Each year, flu strains in the vaccine are selected based on the most commonly circulating flu viruses. The viruses are inactivated, or “killed,” meaning they cannot replicate or cause illness.


Ingredients called adjuvants are added to vaccines to create a stronger immune response and help the vaccine work better. MF59 adjuvant is an oil-in-water emulsion with an excellent safety record that is included in some flu vaccines.


To supply enough flu vaccine for the entire country, some vaccine is stored in multi-dose vials. To prevent contamination and unwanted microbial growth, preservatives are included. The most controversial preservative is thimerosal, a compound containing mercury. Reputable scientific studies have shown that mercury in vaccines is not a cause of autism. Thimerosal is not present in individual-dose flu vaccines.


Sugar or gelatin keep the vaccine effective after manufacture.

Residual materials:

Some ingredients are used to manufacture the vaccine, but not needed for it to work. Despite removal after production, some trace amounts remain in the vaccine, including:

  • Antibiotics that prevent bacterial growth during manufacturing.
  • Inactive ingredients like formaldehyde used during manufacturing to “kill” the virus so it won’t cause disease.
  • Egg protein used to grow the virus.

By combining these ingredients, flu vaccines are made each year according to the strains selected by the World Health Organization. The Centers for Disease Control and Prevention, or CDC, is the authority on vaccines and expresses no preference for one flu vaccine over another. Experts across many fields of study agree that everyone six months and older should receive an annual flu vaccine. Flu vaccines have been shown to reduce the risk of illness, hospitalizations and flu-related death in children. Protecting yourself, your loved ones, and those who cannot be vaccinated is a big priority this season. Your pharmacist or other healthcare provider can provide routine vaccines and travel vaccines you may need, including the flu shot.

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