Dec. 15, 2005 -- An FDA advisory panel backed the approval of the first shingles vaccine Thursday, though for a narrower group of patients than manufacturers had sought.
But experts also strongly urged more studies of how the vaccine works in patients with chronic disease and suppressed immune systems and asked the agency to require manufacturer Merck to carefully monitor safety if it is released to the U.S. market.
The vaccine -- known as Zostavax -- is actually a double dose of chickenpox vaccine. Both shingles and chickenpox are caused by the same virus, called varicella.
Shingles usually occurs in older adults and the immunocompromised and is a reactivation of the chickenpox virus. It can cause chickenpox-like skin blisters that usually appear in a band-like pattern; hence the name "shingles." The rash can cause severe pain, tingling, and numbness in some patients that can last long after the visible rash has resolved.
In trials, the vaccine cut the risk of shingles roughly in half for patients over 60. Patients between 60 and 69 who got the vaccine were nearly two-thirds less likely to develop shingles than patients who got an inert placebo shot, but the treatment was progressively less effective as it was used in older patients.
That fact concerned some experts. People over 80 are at greatest risk for severe pain and chronic nerve pain known as postherpetic neuralgia that can result from shingles.
Merck sought to sell the vaccine to adults over 50 years of age. But members of the advisory panel unanimously recommended that the agency reject that bid because the company did not present clinical evidence that it is safe and effective in patients under 60.
Bonnie M. Word, MD, an assistant professor of pediatrics at Baylor College of Medicine and a member of the expert panel, says Merck was asking for "a leap of faith" concerning use of the vaccine in patients under 60.
"My guess is it will work once the company does the studies but until we have the studies we really can't comment," says David Markovitz, MD, another committee expert.
Experts unanimously backed the vaccine as safe and effective in preventing shingles in patients over 60. Though positive for Merck, the panel made its recommendation considerably narrower than the company had wanted.
Merck had also asked the FDA to approve Zostavax for prevention of postherpetic neuralgia in patients who already have shingles, which can linger for years. The company's data suggested that the vaccine could cut that risk by nearly 40% overall.
But several experts questioned whether trials showed a strong ability to prevent neuralgia itself or whether the effect was mostly due to a lower rate of shingles.
Booster Shot Needed?
Researchers still don't know exactly how the vaccine would be used if the FDA grants approval. The FDA isn't required to follow the recommendations of its advisory panel, but it usually does. Merck's clinical study lasted four years, leaving open questions on whether or not patients may require a booster shot if the vaccine's effect dips after that time.
Experts also asked the FDA to require Merck to study how the vaccine works in patients with suppressed immune systems caused by medical treatments or HIV infection. Those patients are the most vulnerable to debilitating shingles but are also at the highest risk for vaccine complications.
"The concern is that you're talking about giving this to a universally large population without adequate safety data, says Gary D. Overturf, MD, a professor of pediatrics and pathology at the University of New Mexico, and chair of the advisory committee.
Jeffrey Silber, MD, Merck's senior director of clinical research, tells WebMD that the company would begin trials with immunosuppressed patients in 2006. The company also plans to continue its study to find out how long the vaccine's protective ability lasts.
"That question is in the process of being answered but will of course take several years," he says.