A new vaccine may help protect adults from shingles, an intensely painful infection that forced late night talk show host David Letterman off the air for five weeks.

People who've had chickenpox can develop shingles as adults. About one million people in the U.S. develop the rash annually.

The virus responsible for the childhood itchiness, called herpes zoster, may lie dormant until immunity wanes during adulthood.

The same virus causes chickenpox in children and shingles in adults.

In shingles, the virus re-emerges to cause pain, tingling, a rash and blisters that may last for weeks. Two years ago, Letterman joked shingles "hurt so much I was Michael-Jackson crazy."

"It's like somebody took a thousand needles and just stuck 'em right into your rear end all at one time," agreed Lionel Duke, a 76-year-old in San Diego, Calif., who was randomly assigned to receive dummy injections as part of the study.

An experimental vaccine may protect about half of older adults from suffering shingles, according to a study in the June 2 issue of the New England Journal of Medicine.

For three years, Michael Oxman of the VA San Diego Healthcare System and his team studied 38,546 volunteers age 60 and older who had chickenpox as children. Participants received either the vaccine or a placebo.

Among those who received the vaccine, there were 315 cases of shingles, compared to 642 in the placebo group.

The severity of long-term nerve pain from shingles, called postherpetic neuralgia, was also reduced among those who received the vaccine. There were 27 cases of the hard-to-treat pain among those who received the vaccine, versus 80 for placebo recipients.

"Since zoster and ... postherpetic neuralgia are common and serious, it seems prudent to market the zoster vaccine, but only if a large number of those vaccinated are followed closely, particularly those over 85 years of age," wrote Dr. Donald Gilden of the University of Colorado Health Sciences Center in a journal commentary.

Gilden said he endured the rash and pain of shingles for a few days after turning 60.

The few side-effects reported in the study were generally mild, compared to the effects of the virus.

A drug company has applied to have the vaccine approved for use in the U.S. and Europe.