FDA Panel Backs Rotateq

Zostavax is similar to Merck's Varivax vaccine for chickenpox and to the chickenpox component of its recently approved Proquad vaccine, which also protects children against measles, mumps and rubella (German measles).

The FDA staff reviewed Merck's research that says a single dose of Zostavax given to relatively healthy adults age 60 and older showed the vaccine reduced the incidence of shingles and shingles-related pain, known as postherpetic neuralgia, over the first three years following vaccination. Merck's clinical trials covered more than 37,000 people who were tested between November 1998 and April 2004. Some received Zostavax, and others received a placebo.

The FDA report says there is a "trend of decreasing efficacy" in three measurements of how well Zostavax works during the three years after the vaccine is administered. Gauging the effectiveness after three years "is limited by the relatively small proportion of subjects with follow-up," the FDA says.

"Age appears to be an important factor in some study measures of vaccine efficacy," the report adds. For example, shingles was reduced by 63.9% in the 60-69 age group vs. 37.6% in the 70-plus group, but the rates of postherpetic neuralgia were similar in both groups.

There is "a consistent trend toward progressive loss of vaccine efficacy in prevention of [shingles] with increasing age, although the numbers of subjects and cases of [shingles] occurring at the oldest ages are relatively small."

No significant difference between the groups was observed in terms of deaths, hospitalizations, use of pain medications or interference with daily activities, the staff report says.

Because Merck studied relatively healthy people, its research "may not provide an adequate opportunity to evaluate whether the vaccine had any impact" on shingles-related hospitalizations or other severe complications, the FDA report says.

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