Were you looking for information about Zostavax? Zostavac is a common misspelling of Zostavax.
Zostavax® is a shingles vaccine that is approved for people age 50 and over. The vaccine contains a live but weakened version of the varicella-zoster virus. It works by causing the body to produce an immune system response to the virus. Zostavax, which is given as a single injection, is generally effective for four years. Possible side effects of Zostavax include headaches and injection site reactions.
(Click Zostavax for more information on the effects of Zostavax, how the medicine works to prevent shingles, and what you should know before getting the vaccine.)