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Booster shots are additional doses of a vaccine needed periodically to "boost" the immune system.  

Booster shots are additional doses of a [[vaccine]] needed periodically to "boost" the [[immune system]].  

For example, the tetanus and diphtheria (Td) vaccine require booster shots which are recommended for adults every ten years.<ref>http://www.cdc.gov/vaccines/about/terms/glossary.htm#b</ref>

For example, the [[tetanus]] and [[diphtheria]] (Td) vaccine require booster shots which are recommended for adults every ten years.<ref>http://www.cdc.gov/vaccines/about/terms/glossary.htm#b</ref>

==References==

==References==