A study of more than 38,000 people aged 60 or older found that those who received the vaccine, made by Merck & Co., were 51 percent less likely to develop shingles.

The vaccine also reduced the severity of sickness in people who got shingles, and cut by two-thirds the chances of developing longlasting nerve pain.

The vaccine's reach could be huge, considering that shingles affects at least 1 million Americans a year, according to the study in Thursday's New England Journal of Medicine.

Shingles, caused by a reawakening of the chicken pox virus, is particularly a problem for the elderly. The number of cases is expected to grow as more people reach old age.

"I figure if we vaccinated everyone who was 60 or older who hasn't already had shingles, we could expect to reduce the number of cases of shingles in the United States by 250,000 each year and reduce the severity of disease in most of the 250,000 people who did get shingles," said Dr. Michael Oxman, an infectious disease specialist at the VA San Diego Healthcare System who directed the study.

'You Can't Get Beyond It'

Merck submitted an application on April 25 to the Food and Drug Administration seeking approval to market the shingles vaccine. The company said it typically takes about 10 months for the FDA to do its review.

The study, done by Department of Veterans Affairs researchers with help from the National Institutes of Health and Merck, will be included in the licensing review.

"We can have an impact on something that hurts people," said Dr. Stephen Straus, who was lead researcher for the vaccine study at NIH's National Institute of Allergy and Infectious Diseases. "Anyone who knows someone who has had shingles knows this is something you don't want to get."

Mary DeLuca, 82, of Philadelphia, said that when she developed shingles on her scalp about eight years ago, the pain was so bad she could not get out of bed.

She still suffers nerve pain, DeLuca said, and "the doctor told me it's something I'll have to live with for the rest of my life."

Mary Colgan, 78, of Ardmore, Pa., said shingles pain is unlike any other.

"It's very sharp; it's very intense. It takes up all your thinking because the pain is there and you can't get beyond it," said Colgan, who had shingles three years ago.

"I have this vision of the month of January, sitting in my recliner, taking Percocet, eating frozen dinners and watching TV. It's just disabling."

Colgan predicted the vaccine would be popular.

"If they took it to any senior center, people would get in line to get it," she said.

Painful Rash of Blisters

Shingles is caused by the varicella-zoster virus, which also causes chicken pox. After a case of chicken pox, the virus lies dormant in nerve cells along the spinal cord, but it can reemerge years later as shingles.

It isn't fully understood why the virus reactivates, though waning immunity and advancing age are factors. About half of people over 85 get shingles, and people with weakened immune systems from AIDS, cancer and other conditions are at heightened risk.

Children who are vaccinated against chicken pox can still get shingles, but early research indicates that they may be less likely to get shingles or get a milder case.

Shingles usually starts out as a burning or tingling sensation and then progresses into a painful rash of blisters, typically on just one side of the torso or face. Shingles on the face is especially worrisome because it can cause vision and hearing loss.

Anti-viral drugs, if taken early, can help. But about 20 percent of people develop the lingering nerve pain called postherpetic neuralgia. Elderly people are especially vulnerable.

The shingles vaccine is actually a high-test dose -- at least 14 times as potent -- of the same vaccine used to protect children from chicken pox. The vaccine is meant to boost the body's immune system against the varicella-zoster virus, keeping it inactive.

To test the shingles vaccine, researchers gave the shot to 19,270 older people and a dummy vaccine to 19,276 others, many through VA medical centers around the country. They then tracked the volunteers for just over three years on average.

Cut the 'Burden of Illness'

Besides reducing the disease in the vaccinated group, the vaccine cut the "burden of illness" from shingles by 61 percent and the risk of postherpetic neuralgia by 66 percent, the researchers reported. The vaccine was most effective in preventing shingles in people under 70, though it did the best job of reducing the severity of shingles in the oldest volunteers.

Side effects were mostly mild, including tenderness and swelling at the injection site.

Since the study followed people for a few years, it's not known how long-lasting the protective effect will be, Oxman said. Merck and the VA continue to follow patients at 12 of the 22 study locations, said Jeffrey Silber, a Merck vaccine researcher who helped oversee the vaccine testing.

The company has not determined what it would charge for the vaccine. In an editorial accompanying the study, Dr. Donald Gilden, chairman of neurology at the University of Colorado School of Medicine, said the shot's cost-effectiveness should be considered before it is recommended for widespread use. But he predicted that it would be "at least as cost-effective as other currently used vaccines."

Gilden, in an interview, said he knows firsthand the pain of shingles, both as a doctor and a patient.

"I remember it as some of the worst days of my life," he said.