Some vaccines require a booster, while others can last a lifetime.
Even still, with talk of a third shot — a booster shot — for those already vaccinated against COVID-19, some are asking why an additional shot is needed at all if the original vaccination is ‘so effective.’
Vaccine booster shots are common
A booster shot for vaccines is not unusual. Some vaccines, like the one you get for tetanus, need a little boost over time. That’s because the immunity you get from them wanes after a little bit. Anyone who has stepped on a rusty nail has probably been asked by a doctor about their last tetanus shot and received a booster if too much time has passed.
Some need a series of shots to last a lifetime
Some vaccines, like the shots for polio and hepatitis, need multiple doses to give you full protection. Those types of vaccines are called a series. Some of those, but not all, give you lifetime protection against the disease. The measles, mumps and rubella vaccine — also known as the MMR — is a series and gives you lifetime protection against measles and rubella. But you may need a booster shot for mumps, if exposed.
Flu shots are new every year
Other vaccines need to be done more regularly. Doctors recommend you get a flu shot every year, not because your immunity needs a boost, but because you need all new immunity. The flu virus likes to mutate, so new strains tend to circulate from year to year. Each year the vaccine is designed to hopefully target the predominant flu strain.