Were you looking for information about Zostavax? Zostavac vaccine is a common variation and misspelling of Zostavax.
Zostavax® is a single-dose vaccine that is licensed to prevent shingles in people 50 years old and older. It is a live but weakened version of the varicella-zoster virus, which works by causing the body to produce an immune system response to the virus. While most people tolerate Zostavax well, potential side effects may include injection site reactions and headache.
(Click Zostavax for more detailed information on how Zostavax works to prevent shingles, a discussion of the vaccine's effectiveness, and a list of important precautions and warnings to be aware of before getting vaccinated.)