Federal health advisers endorsed a proposed vaccine on Thursday to help prevent shingles, an often-excruciating disease that afflicts as many as 1 million adults every year.
The Food and Drug Administration's advisory panel on vaccines said the vaccine for shingles appeared to be safe and effective in people aged 60 and older. However, panelists worried its effectiveness may not last, and said it appeared to be less effective in people over 80.
The vaccine, Zostavax, was developed by Merck & Co., which sought to have it approved for use in people aged 50 and older.
But Merck conducted trials mostly on people 60 and older, leaving the members of the FDA panel on vaccines uncertain whether it was safe or effective for those in their 50s.
Whether to approve the vaccine for sale is now in the hands of the FDA, which often follows the advice of its advisory panels. Even if the FDA approves it for use only in those 60 and older, doctors could still prescribe it for younger people.
People develop shingles as they age because their immunity to the chickenpox virus wanes. The condition usually starts with pain or itching in a band on the skin, followed by a rash or blisters that can last for days or weeks. It can sometimes cause long-term nerve pain.
"The need is there," Dr. Jeffrey Silber, a senior researcher with Merck, told the FDA panel.
Although they generally supported its use, panelists questioned how long the vaccination would be effective, or whether it would only stave off shingles for a few years.
If its effectiveness does decrease, a patient might have to get a booster or risk becoming more seriously ill with the condition once the vaccine wears off.
Silber said the trials showed the vaccine was effective for at least four years, and studies were ongoing to establish its long-term effectiveness, which remains uncertain.
"This is always a question with every new vaccine," he said.
Panelists wondered about data that suggested its effectiveness decreased in people 70 and older. Dr. Patricia Rohan of the FDA said the trial data showed some drop-off in effectiveness among people over 70 years old.
While most vaccines prevent the body from acquiring an illness, this vaccine is unusual in that it may prevent a flare-up of a virus already in the system.
Panelists called on Merck to conduct additional studies on the vaccine. Zostavax is based on the company's chickenpox vaccine, but is built around a much more potent dose.
The favorable vote is another boost for beleaguered Merck, which also won an endorsement of its new vaccine for rotavirus on Wednesday. Merck is facing thousands of lawsuits over its Vioxx painkiller.
