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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.
ï· When you look at the vaccine schedule, it does sometimes seem like a lot doses of the. same vaccine. ï· The reason for the number of doses needed varies by vaccine. ï· For some vaccines (primarily inactivated vaccines like Hib or PCV13) the first. dose does not provide as much immunity (protection) as possible. So, more doses. are needed. ï· For vaccine such as DTaP, the initial series of 4 shots (generally received at 2, 4, 6, and 12-18 months) helps build immunity. Getting multiple doses allows the. immune response to last longer. ï· After a while the immunity begins to wear off.