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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.


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.


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

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.


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…


An illness or injury that happens suddenly and noticeably.

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…

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