Findings Not Expected to Delay Chickenpox Vaccine Approval
A new analysis of an experimental chickenpox vaccine recorded a slightly higher rate of illness in vaccinated children than found previously but the increase is not expected to delay its approval, Food and Drug Administration officials said Friday.
The research does raise questions, however, about how long immunity from the vaccine lasts and whether additional doses will be needed to protect people from contracting the disease in adulthood, when typically it is far more severe.
Waning immunity is one of the issues that has concerned agency officials in recent years as they have deliberated approval of the vaccine, which was developed by Merck & Co. of New Jersey.
Officials from the FDA’s center for biologics evaluation and research presented the update to the agency’s Vaccines and Related Biologics Advisory Committee. The panel was not asked to make a recommendation and FDA officials refused to predict when approval would come.
Chickenpox, a highly contagious illness characterized by fever, weakness and a body rash that itches and blisters, is a common childhood ailment that afflicts 4 million people annually, most of them children.
It is virtually the only significant childhood ailment for which there is no vaccine available. Vaccines already are in widespread use for diphtheria, tetanus, pertussis (whooping cough), measles, mumps, rubella (German measles) and polio, among others.
A chickenpox vaccine similar to Merck’s is already in use in several other countries.
Dr. Philip Krause of the FDA told the panel the study found that, after five years, 4.3% of those vaccinated individuals came down with the ailment--roughly half the rate at which unvaccinated children contracted the illness. The normal rate in unvaccinated children ranges between 8.3% and 9.1% of the population annually, he said.
Based on the most recent data, the vaccine is 50% to 75% effective, he said.
Significantly, however, vaccinated individuals who got the disease had much milder cases than naturally acquired chickenpox, he said. This raises the possibility that adults vaccinated in childhood who come down with the disease will have milder cases of the disease, although he said “we won’t know for at least another 20 years” as long-term effects become clear.
Once the vaccine is licensed, the agency is likely to insist on long-term post-marketing surveillance to answer lingering questions, he said.
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