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Itâs not entirely clear why the length of acquired protection varies with different vaccines. A single dose of some vaccines provides lifelong immunity, while others require an additional dose (boosters) in order to maintain immunity.tâs not entirely clear why the length of acquired protection varies with different vaccines. A single dose of some vaccines provides lifelong immunity, while others require an additional dose (boosters) in order to maintain immunity.
Vaccines contain ingredients, called antigens, which cause the body to develop immunity. Vaccines also contain very small amounts of other ingredients--all of which play necessary roles either in making the vaccine, or in ensuring that the vaccine is safe and effective.