A vaccine is a biological preparation that provides immunity against one or more diseases. Vaccines contain weakened (attenuated) living germs, killed germs or parts of them, or instructions (mRNA) for the production of antibodies. They also include adjuvants and stabilizers to help them work well, usually aluminum salts.
Live, weakened vaccine viruses typically reproduce fewer than 20 times in the body and then die. When the immune system responds to these attenuated viruses, it produces memory cells that provide long-term protection against those particular virus types. The vaccine also prompts plasma B-cells to create antibodies that can kill the viruses or block them from entering other cells, preventing infection.
Vaccines that use a dead bacteria or virus don’t make people sick and can be used even by those with weakened immune systems. However, these vaccines may require multiple doses to produce strong immunity. Vaccines that take different approaches to targeting specific disease antigens or mechanisms of action can also be created.
Vaccines can prevent serious illness and death. Several diseases have been eliminated in the United States thanks to high vaccination rates. The CDC recommends that everyone receive the recommended vaccines for their age and health status.