What is a vaccine made of?
Vaccines contain an ingredient that trains the immune system, such as a weakened or inactivated germ, a piece of a germ or genetic instructions like mRNA, plus small amounts of ingredients that keep them stable and effective.
The active ingredient is called the antigen, or instructions to make one. Live attenuated vaccines, like measles, mumps and rubella, use weakened germs. Inactivated vaccines, like most flu shots, use killed germs. Subunit vaccines use specific proteins, and mRNA vaccines, like some COVID-19 vaccines, give cells instructions to make a harmless protein.
Other ingredients include adjuvants, such as aluminum salts, which boost the immune response; stabilizers, such as sugars or gelatin, which protect the vaccine during storage; and sometimes preservatives to prevent contamination in multi-dose vials. Most vaccines are mainly water.
Safety testing
Vaccine ingredients are present in very small amounts and are carefully tested in clinical trials before approval. Regulators continue to monitor vaccines after they are introduced. Ingredient lists are publicly available for each approved vaccine.
Did You Know?
mRNA from vaccines breaks down within days and does not enter the cell nucleus or change a person's DNA.