Why do some vaccines require several shots? For some vaccines, a series of shots has a cumulative effect and improves the level of protection against a disease with each dose. For other vaccines, additional shots help account for changes or mutations in some of the disease-causing viruses and bacteria. There are still other vaccines that do not last forever and need periodic booster shots to remain effective.
Posted on: Sat, 31 Aug 2013 22:44:53 +0000
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