British pharmaceutical giant GlaxoSmithKline said Tuesday its experimental shingles vaccine has shown effectiveness across all age groups in ongoing human trials, particularly people over age 70 -- a result that could be a boost for the company's bottom line and a welcome development for those who suffer from the painful condition.

The only vaccine currently approved in the United States, Zostavax, has been shown reduce the occurrence of shingles in a majority of people between ages 50 to 69, but that effectiveness tends to wane among older people, who are at particular risk. By contrast, GSK's "HZ/su" vaccine reduced the risk of shingles by more than 97 percent in adults 50 and older, and the drug showed no drop in efficacy among older age groups, according to the company and results published in the New England Journal of Medicine.

Shingles, which results from the reactivation of a dormant chickenpox virus later in life, usually brings with it a heaping of misery in the form of an itchy, painful skin rash, usually on one side of the body. Nearly 1 in 3 Americans will develop shingles, and an estimated 1 million cases surface in the United States each year, according to the Centers for Disease Control and Prevention. Shingles is not contagious but can spread chickenpox to people who haven't been exposed to the virus.

Shingles typically affects people 50 or older, people with medical conditions that hinder their immune systems or people receiving immune-suppressing drugs for conditions such as cancer. A federal advisory committee has recommended that people 60 and older get a vaccine in order to reduce the risk of shingles and its complications.

GSK's large-scale trial of its vaccine involved more than 15,000 patients age 50 and older in more than a dozen countries. The vaccine, which was given in two doses, reduced the risk of shingles by 97.2 percent compared to a placebo, the company said. The most common side effects were redness and swelling at the injection site, as well as muscle pain and headache, according to the study.

GSK has said it sees "significant potential" for its vaccine, which if approved could cut into the hefty revenue generated by Zostavax, produced by Merck. For now, the company said it plans to conduct additional trials to evaluate the ability of its vaccine to prevent shingles among people older than 70 and in adults with weakened immune systems.