While shingles responds readily in some patients to treatment with acyclovir, an antiviral drug, it can prove recalcitrant and difficult to treat in many others. The disorder is considered a major public health concern, affecting an estimated 600,000 to 1 million people annually

Varicella zoster, the microbe that causes both shingles and chicken pox, retreats after a childhood bout with the itchy and blistering condition, only to resurface decades later as shingles, a nerve-damaging disorder that sometimes is so painful that some people have considered suicide. Varicella zoster is a member of the herpes family.

"This is a landmark study and the largest vaccine study in the world," Dr. Shing-shing Yeh, a physician and researcher at the Northport Veterans Affairs Medical Center on Long Island said Wednesday.

Virus Remains Dormant in Nerve Cells

Doctors from 22 VA medical centers nationwide participated in the trial, which included more than 38,000 participants whose average age was 69.

"Shingles is a common and painful disease for anyone who has had chickenpox when they were young. The virus remains dormant in nerve cells," Yeh said.

However, shingles has been known to occur in children as young as 3, explained Dr. Stephen Straus, a senior scientist at the National Institute of Allergy and Infectious Diseases. But shingles pain becomes far more intense with age.

Strauss said doctors can tell the difference between the eruptions of chicken pox and shingles by how the rashes appear.

In chicken pox, the virus is carried by the bloodstream, prompting rashes and blistering are all over the body. In shingles, the eruptions follow the path of the damaged nerve.

Straus said it is important to seek treatment. When the eruptions are on the face, the virus can spread to the eyes and cause blindness.

About half of all people age 85 will develop the disorder.

Seeking FDA Approval

Writing in Thursday's New England Journal of Medicine, researchers reported that the experimental vaccine, a product of Merck Corp., promises to prevent the disorder altogether. It reduced the incidence of shingles by 51 percent.

A second, more debilitating shingles-related condition, post-herpetic neuralgia, which is pain radiating from severely damaged nerves, was reduced by 66 percent, Yeh said.

During the trial, patients received either the vaccine or a placebo. In the placebo group, 642 cases of shingles were diagnosed but only 315 were diagnosed among vaccinated patients. The vaccine is a version of the live-virus chicken pox vaccine that has been administered to children since 1995.

Christine Fanelli, a spokeswoman for Merck Vaccines, said the company is seeking Food and Drug Administration approval of the shingles shot. "We did that on April 25, looking at what we think is a 10-month window for an FDA action," she said.

She said Merck expects word from the agency sometime next spring.

Prevalence of Shingles Likely to Increase

"For some people, shingles can result in months or even years of misery," said Michael Oxman, an infectious disease specialist at the San Diego VA Healthcare System and the University of California, San Diego, and the study's lead investigator.

While shingles responds readily in some patients to treatment with acyclovir, an antiviral drug, it can prove recalcitrant and difficult to treat in many others. The disorder is considered a major public health concern, affecting an estimated 600,000 to 1 million people annually, according government health statistics.

"As people live longer, and the proportion of older people in our population increases, it is highly likely that the prevalence of shingles will increase. A preventive shingles vaccine would be an enormous boon for the health and quality of life of seniors," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

For most people, shingles first manifests as pain, itching or tingling in an area of skin on one side of the body or face, doctors said Wednesday. But a painful blistering rash can follow and take weeks to months to heal. For some people the condition causes so much discomfort that even a mild breeze or light clothing can cause excuciating pain.

However, Straus said the study helped doctors learn that shingles-related pain occurs over a wide spectrum and that some patients have no discomfort whatsoever.