WASHINGTON (AP) _ A vaccine for older people who want to prevent shingles _ the painful resurgence of the chickenpox virus that afflicts 1 million Americans a year _ appears to keep the illness in check for many who receive it, according to government scientists.
Federal health advisers reviewed the experimental vaccine Thursday, and were expected to vote later in the day on whether it appears to be safe and effective. A positive vote would move the vaccine a step closer to approval, but the Food and Drug Administration makes the final call.
The vaccine, Zostavax, was developed by Merck & Co. It is based on the company's chickenpox vaccine, but is built around a much more potent dose. 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.
In its submission to the FDA, Merck said trials showed the vaccine ``significantly reduced the burden of illness'' arising from shingles. Compared to those taking a placebo, 51 percent fewer people who received the vaccine developed shingles, and those that did reported less severe cases.
Merck wants the vaccine to be available to people over 50 who had the chickenpox when they were younger.
``The need is there,'' Dr. Jeffrey Silber of Merck told the FDA's advisory panel.
But some panelists questioned whether it was in fact effective in the oldest of people taking the vaccine.
Dr. Patricia Rohan of the FDA said the trial data showed some drop-off in effectiveness among people over 70 and 80 years old.
People develop shingles as they age because their immunity to the dormant chickenpox virus wanes. The virus hides in the nerves, and shingles 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.
A case of shingles usually protects against another attack.
The FDA vaccine advisory panel's consideration of Zostavax comes after the panel found that Merck's experimental vaccine for rotavirus, a potentially fatal diarrheal infection in infants, is safe and effective, overruling safety concerns that were tied to a competitor's vaccine that caused it to be pulled from the market in 1999.
The move puts Merck's RotaTeq a step closer to approval for general use in infants. Rotavirus hospitalizes thousands of American children with diarrhea and kills millions in developing countries.
In the United States, rotavirus infects many children before their third birthday, sometimes resulting in hospitalization. The virus kills several dozen American children a year, but most children eventually develop an immunity.
In developing countries with less medical care, rotavirus is much more dangerous, killing one child in 250.
Wednesday, the FDA advisers expressed some wariness about approving the vaccine in the face of problems tied to the earlier vaccine, RotaShield, which manufacturer Wyeth pulled in 1999 after 20 infants developed a potentially fatal bowel condition within a month of receiving it. More than 1 million received it.
Researchers in the Rotateq trials looked closely for cases of children developing the condition, called intussusception, and found it did not occur more often than in children who received a placebo instead of the vaccine.