A live attenuated varicella-zoster vaccine (Zostavax--Merck) has been approved 
by the FDA for prevention of herpes zoster (HZ; zoster; shingles) in persons > 
or = 60 years old. Each dose of Zostavax contains about 14 times as much 
varicella-zoster virus (VZV) as Varivax, which has been used in the US since 
1995 to vaccinate against varicella (chicken pox).