The vaccine already was approved for people age 60 and older. The approval is based on a Merck clinical trial that showed the vaccine to be about 70% effective in preventing shingles in the younger age group.
The study also found that even when vaccinated 50-somethings did get shingles, they suffered far less pain and far shorter bouts of the painful, sometimes disabling disease.
"The likelihood of shingles increases with age. The availability of Zostavax to a younger age group provides an additional opportunity to prevent this often painful and debilitating disease," Karen Midthun, MD, director of FDA's Center for Biologics Evaluation and Research, says in a news release.
Shingles -- known to doctors as herpes zoster-- is caused by the same herpes virus that causes chickenpox: varicella zoster. But when chickenpox gets better, the virus doesn't go away. It hides in nerve roots. When reactivated in later years, the virus erupts into extremely painful shingles-like lesions.
Why get vaccinated at age 50? That's when shingles risk shoots up. Before age 50, about two people in a thousand get shingles. After age 50, about six people in a thousand get shingles. A person's lifetime risk of shingles is about 30%.
Even people who already have had shingles can get it again. Their risk of a second case is about the same as the risk of getting a first case.
The biggest drawback to Zostavax is its cost. The catalog price is about $161.50, about 10 to 20 times the cost of flu vaccine.