By John J Lumpkin
Washington - A vaccine for older people who want to prevent shingles, a painful resurgence of the chickenpox virus that mainly afflicts people age 50 or over, appears capable of keeping the illness in check for many who receive it, according to government scientists.
Federal health advisers will review the experimental vaccine on Thursday and possibly recommend to the Food and Drug Administration whether it should be approved for sale.
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. Those who did reported less severe cases.
Merck wants the vaccine to be available to people over 50 who had chickenpox when they were young. In documents posted on the FDA's website, agency reviewers noted the vaccine seemed less effective in people over 70.
People develop shingles as they age because their immunity to the dormant chickenpox virus wanes. The virus hides in the nerves and 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 is considering Zostavax after it found Merck's experimental vaccine for rotavirus, a potentially fatal diarrheal infection in infants, to be safe and effective, overruling safety problems 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; it kills millions in poor countries.
Still, members of the vaccine panel worried about trial data that showed a few more children who took the vaccine developed seizures than did those who took a placebo. It was unclear whether the vaccine played a role.
The FDA is not bound by decisions of its advisory committees, but it often follows their recommendations.
Merck officials said they would conduct a follow-up study to track any long-term effects of the vaccine, which has been in development since 1993.
In the United States, rotavirus infects many children before their third birthday, sometimes resulting in admission to hospital. The virus kills several dozen American children a year, but most children eventually develop an immunity.
In poor countries with less medical care, rotavirus kills one child in 250.
On Wednesday, FDA advisers expressed 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 died from the bowel condition within a month of receiving it. More than one 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. - Sapa-AP