A new vaccine that could put the pox on shingles for many adult sufferers of the often painful infection caused by the chickenpox virus has received federal approval, its manufacturer said Friday.

Merck & Co. Inc. (MRK) spokeswoman Christine Fanelle said the vaccine, Zostavax, was approved late Thursday by the Food and Drug Administration. The vaccine is only for adults who previously have had chickenpox.

Shingles, also called herpes zoster, strikes when the chickenpox virus reactivates and resumes reproducing after lying dormant for decades in nerve cells in the body.

There are roughly 1 million new U.S. cases of shingles each year. It typically affects the elderly, though anyone with a weakened immune system is vulnerable.

Shingles can cause itching, burning and tingling, as well as a distinctive red rash that develops into pus-filled blisters that later break open and form scabs. Pain, too, is common and can persist in some patients for months or years.

Merck research showed the vaccine reduced the incidence of shingles by half and pain and discomfort by nearly two-thirds.

The vaccine's long-term effectiveness remains unclear. Merck has shown that it works for at least four years, and plans to track patients for a decade.

The vaccine is intended for use in people 60 and older. "This is going to be the first product of any kind, vaccine or anything else, that can prevent shingles," said Dr. Jeffrey Silber, senior director of clinical research on biologics and vaccines for Merck Research Laboratories.

Zostavax is based on Merck's chickenpox vaccine, Varivax, but is 14 times more potent. The FDA approved Varivax in 1995. A majority of American children now receive that vaccine.

Anyone who has had chickenpox can develop shingles. Merck estimates that half of all people who reach age 85 will develop shingles during their lifetime.

Shingles can't be passed from human to human, but anyone who hasn't had chickenpox — or never received the vaccine that protects against it — can be infected with the virus if exposed to someone with an active case of shingles.

The approval is welcome news for Merck, which faces thousands of lawsuits over its withdrawn painkiller Vioxx. It's also just one of several vaccines for which the Whitehouse Station, N.J. company has received — or soon expects to receive — FDA approval.

They include RotaTeq, a vaccine against a common, sometimes dangerous gastrointestinal virus in children, approved in February; and ProQuad, a combined vaccine against measles, mumps, rubella and chickenpox, approved in September.

And early in June, Merck hopes the FDA will approve its Gardasil vaccine against human papillomavirus, the main cause of cervical cancer.

European and Australian health officials earlier this month approved the shingles vaccine, Merck said.

The company is eyeing the roughly 50 million Americans and 100 million Europeans age 60 and older as its market for the single-dose vaccine.

A dose will cost $152.50.