Vaccinating adults with a concentrated version of the children's chickenpox vaccine can halve the risk of developing shingles, an intensely painful disease that affects as many as 1 million people in the United States each year.
The vaccine, studied in a clinical trial involving about 39,000 Americans 60 and older, also significantly reduced the pain associated with shingles and lowered by 67% a serious complication of shingles, postherpetic neuralgia, which can linger for years.
Postherpetic neuralgia, affecting about 40% of shingles patients older than 60, can cause excruciating pain from a light brush of clothing or a gust of wind. The complication is not easily managed with medication.
Merck & Co., the maker of the vaccine, has applied to the Food and Drug Administration for approval and could receive a decision within a year.
Doctors said the vaccine, which had been in development for 18 years, could become a standard preventive treatment for most adults older than 50, the group affected the most by shingles.
The study's findings were published today in the New England Journal of Medicine.
Medical experts said the results from the vaccine trial were timely because the rate of shingles was expected to increase, in part because of the graying of the U.S. population.
"I have had many patients who have had pain for years -- it changed their entire quality of life," said Dr. Donald Gilden, neurology department chairman at the University of Colorado Health Sciences Center in Denver who wrote a commentary accompanying the study. "People with shingles and postherpetic neuralgia live in pain every day, and if we could reduce that by 50% or more, that would be wonderful."
Shingles, technically known as herpes zoster, is caused by the varicella-zoster virus, the same virus responsible for chickenpox.
It occurs because the virus is never fully eradicated from the body after a childhood chickenpox infection. Instead, it takes up residence in bundles of nerves known as the sensory ganglia, clustered along the length of the spine.
The virus remains dormant in the ganglia for decades. But later in life, as immunity to the chickenpox virus erodes, it can sometimes reawaken in one of the ganglia and start replicating for reasons that are unclear.
When this happens, the virus particles travel along sensory nerves that project onto the skin and cause a cluster of painful welts. The rash usually does not spread to other regions of the body, although it can in patients with immune deficiencies. People rarely have more than one bout of shingles.
Antiviral medication, if given early enough, can shorten the duration of outbreaks. But other than that, patients usually have to wait for the rash to run its course, which usually takes several weeks.
The study, conducted by the Department of Veterans Affairs, took place at 22 medical centers across the country, enrolling 38,546 men and women. Half the subjects were vaccinated with the shingles vaccine, called Zostavax, and the other half with a placebo.
Zostavax consists of the same weakened virus used in the chickenpox vaccine, which has been approved for use in the U.S. since 1995. It has been administered so far to 53 million children worldwide. Zostavax, however, is 14 times more potent than the children's vaccine, Varivax.
Participants were tracked for an average of about three years, during which the incidence of shingles and postherpetic neuralgia were monitored. Participants answered questionnaires to rank the level of shingles-associated pain. Neither the patient nor doctor knew who was getting the placebo.
There were 957 reported cases of shingles during the study, 315 in the vaccine group and 642 in the placebo group. There were 107 cases of postherpetic neuralgia, 27 among vaccine recipients.
Overall, the scientists calculated that the vaccine reduced the "burden of illness" due to shingles -- a measure including pain and the incidence of the disease -- by 61%.
Side effects of the vaccine were minor, consisting of swelling and rashes around the injection site in 48% of the vaccinated patients compared with 17% in the placebo group. There was no increase in rate of death or serious medical event in the group receiving the vaccine.
Dr. Michael Oxman, an infectious-disease specialist at the San Diego Veterans Affairs Healthcare System and the principal investigator in the study, said researchers still didn't know how long the vaccine's protection would last.
"We've tracked them for long enough to know the vaccine has a very major effect on shingles and postherpetic neuralgia, but ... are they going to need boosters?" Oxman said. "The only way to find out is to track them longer ... We're planning to do that."