FRIDAY, May 26 (HealthDay News) -- Merck's Zostavax vaccine has been approved by the U.S. Food and Drug Administration to prevent shingles in people older than 60, the agency said Friday.

Shingles, caused by reactivation of the same varicella-zoster virus responsible for chickenpox, is characterized by clusters of painful blisters on one side of the body. Anyone who has had chickenpox can get shingles, which affects about 1 in 5 Americans, the FDA said. About 1 million cases are recorded among seniors each year in the United States, Merck said.

Zostavax, a live virus vaccine, reduced the shingles rate by 50 percent among 38,000 older Americans who participated in clinical testing, the FDA said.

Common side effects included redness, pain, and tenderness, injection-site swelling, itching, and headache. Merck said people with a history of leukemia, lymphoma, AIDS, or active tuberculosis should not be given the vaccine.

The FDA said it had asked Merck to conduct additional safety testing, since a small percentage of patients showed "serious adverse events" including aggravated asthma and anaphylactic reaction during clinical trials.

More information

To learn more about shingles, visit the U.S. National Institute of Neurological Disorders and Stroke.