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Active immunity

When you are protected against a disease because your immune system is making antibodies to fight that disease. People get active immunity one of two ways, either by getting the disease or through vaccination. Active immunity is sometimes permanent, meaning a person is protected from the disease for the rest of their life.


An illness or injury that happens suddenly and noticeably.


Adjuvants are “booster” ingredients – they help your body produce a stronger immune response which means greater protection against a disease. The advantage of adjuvants is that they help produce more antibodies and longer-lasting immunity so a smaller amount of the virus or bacteria needs to be used in the vaccine.

Adverse events

An “adverse event” is any health problem that happens after a shot or other vaccine. An adverse event might be truly caused by a vaccine, or it might be pure coincidence.

Advisory Committee on Immunization Practices (ACIP)

A group of medical and public health experts who develop recommendations on the use of vaccines in the United States. The members of this committee are not government employees.


When your body has an exaggerated response to a substance (e.g., food or drug). Also known as hypersensitivity.


An immediate and severe allergic reaction to a substance (e.g., food or drugs). Symptoms of anaphylaxis include breathing difficulties, loss of consciousness and a drop in blood pressure. This condition can be fatal and requires immediate medical attention.


A medicine that fights bacteria.


An antibody is part of the immune system that recognizes foreign substances like bacteria and viruses (antigens) and fights them. Once an antibody encounters an antigen it will remember that antigen and protect against future attacks.


Foreign substance (e.g., bacteria or viruses) that is capable of causing an immune response in the body. The presence of antigens in the body triggers the immune system to act, usually producing antibodies and other immune cells.


A solution of antibodies against a toxin. Antitoxins give passive immunity and can help treat diseases caused by toxins.


Literally “against-virus” — any medicine capable of destroying,  weakening, or treating a virus.

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