What is a booster vaccination?

A boosting effect: Boosters give a boost or increased immune response to a previous series of shots. For instance, every baby gets vaccine series for tetanus, diptheria and pertussis. The effects wane over time so every 5-10 years we need a boost to that effect with another shot. Other vaccines are not boosters - the 2nd MMR and chicken pox are examples. They convert the 10% people who didnt respond to the 1st.

Vaccines: A booster vaccination is given as a follow up vaccine to augment the effects of the original series. Immune responses may wane to a particular vaccine and by giving a booster this can help maintain the effectiveness.