GlaxoSmithKline said Wednesday that its shingles vaccine Shingrix produced a strong immune response in adults 65 and older who had previously been vaccinated against shingles with Merck's vaccine, Zostavax.

GSK filed in October for U.S. regulatory approval to commercialize Shingrix. A decision by the Food and Drug Administration is expected later this year.

Scientific data published in the New England Journal of Medicine in September showed that the effectiveness of Merck's vaccine wanes over time, and that GSK's experimental vaccine appears to have longer-lasting protection.

The question arose: Can people who received Merck's vaccine, the only one approved for the herpes zoster (shingles) virus, later receive the Shingrix vaccine?

"The answer is yes. Our data show that you can do it safely and effectively," said Leonard Friedland, GSK director of scientific affairs and public health for vaccines.

That's important, GSK says, because there are one million U.S. cases of shingles every year. Older adults have a 1-in-3 chance of getting the virus.

In GSK's latest study, presented Wednesday at a meeting with the Centers for Disease Control and Prevention in Atlanta, 430 adults who received the Merck vaccine five years ago were revaccinated with GSK's vaccine, administered in two doses, two months apart, with no serious side effects. The immune response was similar to the company's earlier studies, which showed a high degree of efficacy against shingles, Friedland said.

"This looks to be a very important vaccine," said William Schaffner, an infectious-disease specialist at Vanderbilt University Medical Center. "We all are looking forward to its licensure,"

Data reported in the New England Journal showed that in adults 70 and older, two doses of the GSK vaccine demonstrated 90 percent protection compared with a placebo. The efficacy of the GSK vaccine went down only slightly, from 90 percent to 88 percent, four years after people were vaccinated.

By contrast, the effectiveness of Merck's vaccine was found, in a Kaiser Permanente study of adults 60 years and older, to decrease from 68.7 percent initially to 4.2 percent in the eighth year after vaccination.

"Given the limited efficacy and duration of Zostavax, newer vaccine formulations with improved efficacy are welcome," a New England Journal editorial said

The GSK vaccine has no major safety issues, but has more of an ouch factor at time of injection, noted Schaffner, who said he has no financial ties to GSK or involvement in the studies. "When it goes in, it hurts more than the Merck vaccine," he said. "You'll get a little more redness. This doesn't apply to everyone."

Shingles can recur, and you are not protected just because you had it once. "The virus is always there in our body. You can get it again and again because the body's immune system has declined," Friedland said.

Shingles usually occurs after age 50 and is related to the childhood illness chicken pox. After the itchy blisters of chicken pox disappear, the virus goes dormant in nerve cells. Years later, it can reactivate as shingles. Adults' immune systems to protect against diseases decline with age.

People who live to 85 have a 50-50 chance of developing shingles, which can result in a complication called postherpetic neuralgia, a debilitating nerve pain. Shingles typically shows up as a painful, itchy rash that develops on one side of the body.

GSK employs about 5,000 in the Philadelphia area, at the Navy Yard and in Upper Merion and Upper Providence in Montgomery County.