What Ingredients Are in a Flu Shot?
There are many options when you get a flu shot, so it is a good idea to be familiar with the ingredients. You can choose vaccines with live or inactivated viruses, egg-free, preservative-free, high-dose vaccines, trivalent or quadrivalent, and more.
In the United States, health officials withdrew approval for the FluMust flu vaccine, which is a nasal spray that contains a live attenuated influenza virus, because it was not effective in the last 3 flu seasons.
Below is a list of ingredients you may find in a flu vaccine.
Flu Viruses
You have two options when you get a flu shot — a vaccine that contains an inactivated (dead) flu virus that can’t cause the flu, or a vaccine that contains a live attenuated (weakened) flu virus that sometimes causes a mild infection.
Normal flu vaccines contain 15 micrograms of hemagglutinin (HA) per virus in the vaccine. HA is the flu virus protein that triggers an immune response in the body.
In general, Trivalent flu vaccines contain 3 viruses, with a total of 45 mcg of HA, and Quadrivalent flu vaccines contain 4 viruses, with a total of 60 mcg of HA.
The exception is FluZone, which is a higher-dose flu vaccine for older adults that contains 60 mcg of HA for each of the 3 viruses in the vaccine, for a total of 180 mcg of HA in a single dose of the vaccine.
Egg Protein
Flu vaccines are usually created by growing influenza viruses inside fertilized chicken eggs, harvesting the viruses from the egg, and inactivating the virus with formaldehyde so that it can’t cause infection. The finished vaccine may have small amounts of leftover egg protein.
Animal Protein
For people who are allergic to eggs, there is now another flu vaccine called Flucelvax that is grown in animal cells instead of eggs. Flucelvax is made from kidney cells from a dog that are grown in a laboratory — specifically the Madin-Darby canine kidney epithelial cells (MDCK) that came from a female Cocker Spaniel in 1958.
Preservatives
Thimerosal is a mercury-based preservative that is used in multi-dose vials of vaccines to prevent bacteria, fungi, and germs from spoiling the vial with each use. There is no scientific evidence that thimerosal causes problems for children or pregnant women, but even so, thimerosal has been removed from all childhood vaccines since 2001. There are thimerosal-free flu vaccines for people who are concerned.
Stabilizers
Vaccines contain stabilizer ingredients to prevent the loss of potency over time, even when exposed to heat and light. Vaccines may contain sucrose (table sugar), sorbitol (artificial sweetener), or monosodium glutamate (MSG). Although some people are sensitive to these ingredients, the amounts found in flu vaccines is still very small.
Antibiotics
Most flu vaccines contain low amounts of the antibiotics neomycin, gentamicin, or others to prevent bacterial growth in the vaccine.
Formaldehyde
Formaldehyde is a used in flu vaccines to inactivate influenza viruses that have been harvested from eggs or animal cells. In large doses, formaldehyde is a known carcinogen (cancer-causing chemical). It can also irritate the eyes, nose, throat, or lungs. Most of the formaldehyde is removed before the finished flu vaccine is sent to a pharmacy.
