WASHINGTON (AP) – A new and more potent version of the chickenpox vaccine has won federal approval to prevent shingles, the often excruciatingly painful disease that can strike the elderly when the chickenpox virus emerges after lying dormant for decades.

The Food and Drug Administration announced Friday that it had licensed the vaccine, Zostavax, to reduce the risk of shingles in adults 60 and older. The Merck & Co. Inc. vaccine is only for adults who previously have had chickenpox.

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. The vaccine is not meant for anyone with HIV or who is on immune-suppressing drugs, including transplant patients, said Norman Baylor, director of the FDA’s Office of Vaccines Research and Review.

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 can persist in some patients for months or years.

“This vaccine gives health care providers an important tool that can help prevent an illness that affects many older Americans and often results in significant chronic pain,” said Dr. Jesse Goodman, director of the FDA’s Center for Biologics Evaluation and Research.

Shingles, also called herpes zoster, occurs when the chickenpox virus reactivates and resumes reproducing after a long dormancy in nerve cells in the body.

Zostavax does not prevent the initial infection by the virus, nor does it treat active cases of shingles. Instead, the vaccine helps prevent the reemergence or resurgence of the virus by boosting a patient’s immunity, Goodman said.

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

“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.

Sharon Smith, 68, of Portland, Ore., participated in the Zostavax trials in March 2000, but she received a placebo, or dummy injection, instead of the actual vaccine. That October, she developed shingles. After two emergency room visits and a short hospital stay, Smith remained on pain medication until May 2001, when her searing pain finally ebbed.

“I used to say it was like someone pouring hot oil over my head. At points, I would be stricken with this pain after the initial shingles began, it would just literally bring me to my knees. It was almost indescribable,” Smith said. She added: “I didn’t know you got over it. That is a very devastating thought, that you could be facing that pain forever. It could ruin your life.”

Zostavax is based on Merck’s chickenpox vaccine, Varivax, but is 14 times more potent. The FDA approved Varivax in 1995 and a majority of American children now receive it.

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.

The vaccine’s long-term effectiveness remains unclear. Merck has shown that it works for at least four years, and the company plans to track patients for a decade. Merck also pledged to further study the vaccine’s safety after patients in clinical trials suffered a slightly higher number of serious side effects than did those who received dummy injections, the FDA said. Currently, there is no evidence the vaccine was to blame, the agency added.

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 largest markets for the single-dose vaccine.

The vaccine could become a $1 billion or more a year seller for Merck, said analyst Steve Brozak, with WBB Securities in Westfield, N.J. A dose will cost $152.50.

“Anything that doesn’t have to do with Vioxx should be perceived as good news,” said Brozak, adding that the approval is a “breath of fresh air” for the company.

Merck shares rose 17 cents to close at $34.56 on the New York Stock Exchange.

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On the Net:

Food and Drug Administration: http://www.fda.gov/

Merck & Co. Inc.: http://www.merck.com/

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