What does the term "booster" refer to in vaccination?

The term "booster" in vaccination specifically refers to a subsequent dose given after the initial vaccination series. This additional dose is designed to enhance or prolong the immune response that may diminish over time.

When a person receives a primary vaccine, their immune system responds by producing antibodies and memory cells specific to the pathogen. However, the level of these antibodies can decrease, leading to reduced immunity. The booster dose serves to remind the immune system to produce more antibodies, thus reinforcing and prolonging the protective immune response against that particular disease.

In contrast, preliminary doses initiate the immune response and are not classified as boosters. Vaccines given during an epidemic may be given to large populations to control outbreaks but are not specific to the concept of boosting immunity after initial vaccination. A combination of multiple vaccines refers to polyvaccines or combination vaccines and does not pertain to the boosting effect of an additional dose of the same vaccine.