Why do some vaccines need boosters years later?
Quick Answer
Immunity can fade over time as antibody levels drop and circulating immune cells decline. Boosters re-stimulate the immune system so it makes more antibodies and memory cells.
The Full Story
After some vaccines, antibody levels naturally fall over months or years even though some immune memory remains. A booster dose reminds the immune system of the target and can sharply increase protection. Tetanus vaccines are a classic example: adults in many countries are advised to get a booster about every 10 years. Boosters are also used when germs mutate, as with updated seasonal flu vaccines. The need for a booster depends on the disease, the vaccine type, and how durable the immune response is.
Key Facts
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