Seven-Year Follow-Up Of Vaccine Confirms Long-Term Protection.(Brief Article)

2001 AUG 22 - (NewsRx.com & NewsRx.net) --

by N.R. Saltmarsh, staff medical writer - Children who are vaccinated against varicella and then exposed to the disease in their household have only a 10% chance of being infected, compared with a transmission rate of almost 87% in unvaccinated children, researchers at Oka/Merck have found.

S.J. Vessey and colleagues conducted a seven-year follow-up in vaccine recipients to find out how long vaccine protection persisted.

The researchers studied antibody persistence, breakthrough infection, and household exposure to varicella in the subjects who had been one to 12 years old when vaccinated. Their results were published in the Journal of Pediatrics.

At six years, the antibody persistence rate was 99.5%, reported Vessey and coworkers. After seven years, the annual breakthrough rate ranged from 0.2% to 2.3% and the estimated cumulative event rate was 6.5%. That yielded an estimated vaccine efficacy of 93.8% to 94.6%, when expected annual incidence rates in unvaccinated children were considered, they noted.

Eighty vaccinated children were exposed to varicella in the household, but only eight were infected, Vessey and team found. When compared with the historical attack rate of 86.8% in unvaccinated susceptible people exposed to varicella in the household, vaccine efficacy was estimated to be 88.5%.