UPDATE: Merck Study: No Significant Safety Risk For Shingles Vaccine

A new study designed to answer questions about the safety of Merck & Co.'s (MRK) shingles vaccine suggests it doesn't significantly increase the risk of serious side effects.

The Merck-sponsored study of nearly 12,000 people ages 60 and older did find a higher rate of serious adverse events among recipients of the vaccine, Zostavax, than among those who got a fake shot, or placebo. However, the difference wasn't statistically significant, which means it could have been due to chance.

The Zostavax "and placebo groups had similar safety profiles" both in the six weeks and six months following vaccination, according to a summary posted online by the Journal of the American Geriatrics Society. Results also have been posted on the online government database clinicaltrials.gov. Full results are scheduled to be presented May 13 at the geriatrics society's annual scientific meeting in Orlando, Fla.

A Merck spokeswoman said the company couldn't discuss the safety results until they're presented at the medical conference.

Zostavax, which Merck started selling in 2006, was shown in an earlier study to reduce the occurrence of shingles among people 60 and older by about 50%. Shingles is a nerve and skin disorder that results from reactivation of the virus that causes chickenpox; shingles also can lead to a painful condition called postherpetic neuralgia.

Previous clinical-trial data have sent mixed signals about Zostavax's safety. A large study to prove Zostavax's efficacy, which was published in The New England Journal of Medicine in 2005, found that the overall rate of serious adverse events among vaccine recipients was similar to those on placebo--suggesting the shot was safe.

But a pre-specified safety analysis of a smaller group of participants in the same study found a higher risk of serious events, including heart-related problems associated with Zostavax. The prescribing label for Zostavax warns about this apparent risk.

Some researchers have said the safety risk in the subgroup study was an aberration because there was no pattern to the adverse events that would indicate the vaccine caused the problems. Still, some doctors have remained cautious about recommending the shot.

To address the uncertainty, Merck conducted a new study specifically designed to assess safety. The trial enrolled and tracked nearly 12,000 people in the U.S., Canada and Europe between September 2007 and January 2009. Roughly half received Zostavax and the other half got placebo shots.

At 42 days post-vaccination, the Zostavax recipients experienced 84 serious adverse events, which were defined to include those resulting in death, hospitalization, cancer and other events. There were 67 such events in the placebo group. The risk of serious adverse events among Zostavax users was 1.4%, versus 1.1% in the placebo group, a statistically insignificant difference.

At six months following vaccination, some 340 serious adverse events were reported in the Zostavax group, a rate of 5.7%, versus 300 in placebo, or 5%, also a statistically insignificant difference.

There were 24 fatal serious adverse events in the Zostavax group and 17 in the placebo group, but researchers didn't deem any of the deaths to be vaccine-related. One doctor said he still has concerns about a potential safety risk with Zostavax. C. Bernie Good, professor of medicine at the University of Pittsburgh, said he was concerned about the higher number of deaths and serious adverse events in the Zostavax arm, even though the difference was statistically insignificant.

Good, who treats older patients, said the new study doesn't change his policy of not routinely recommending the vaccine. "Rather I will discuss both the absolute benefits, with the absolute harms that we have from both studies," he said. "Based on that information, some patients will choose the vaccine, and others will decide to pass on it. Neither patient will be wrong in their choice."

Merck's Zostavax sales declined 11% to $277 million for 2009, as a manufacturing snafu constrained supplies. Merck says it's working to resolve the supply problems, but it has put off launching Zostavax outside the U.S. until 2011.

Merck also is seeking to widen the market for Zostavax. It expects to file for regulatory approval sometime this year to market the vaccine to people ages 50 to 59, an age group for which it's currently not approved, even though risk for shingles begins to rise substantially at age 50.

Merck shares dropped 3.6% to $34.32 Thursday amid a broader market downturn.

-By Peter Loftus, Dow Jones Newswires; 215-656-8289; [e-mail]