Measles epidemic in Romania, 1996-1998: assessment of vaccine effectiveness by case-control and cohort studies

Abstract

A measles epidemic occurred in Romania with 32,915 cases and 21 deaths reported between November 1996 and June 1998, despite high vaccination coverage since the early 1980s. Most cases were unvaccinated children aged <2 years and vaccinated school-aged children. A case-control study among preschool children and a cohort study among primary-school children were conducted to estimate effectiveness of Romanian-produced measles vaccine, and to evaluate age at vaccination and waning immunity as risk factors for vaccine failure. Both studies indicated that measles vaccine was highly effective. One dose reduced the risk for measles by 89% (95% confidence interval (CI) 85, 91); two doses reduced the risk by 96% (95% CI 92, 98). Children vaccinated at <1 year of age were not at increased risk for measles compared with children vaccinated at > or =1 year. Waning immunity was not identified as a risk factor since vaccine effectiveness was similar for children vaccinated 6-8, 9-11, and 12-14 years in the past. Because specific groups were not at risk for vaccine failure, an immunization campaign that targets all school-aged children who lack two doses may be an effective strategy for preventing outbreaks. A mass campaign followed by increased first-dose coverage should provide the population immunity required to interrupt indigenous measles virus transmission in Romania.

PIP: Two studies examined the effectiveness of measles vaccines in Romania during the measles epidemic between 1996 and 1998. A case control study among preschool children and a cohort study among primary school children were conducted to estimate Romanian-produced vaccine effectiveness and to identify risk factors for measles among these age groups. Both studies found that measles vaccine was highly effective. Single-dose vaccine effectiveness was 89% and double-dose vaccine effectiveness was 96%. Univariate analysis of the case-control study indicated that being unvaccinated and being born of itinerant parents were significant risk factors for measles among preschool children. Children vaccinated at less than 1 year of age were not at increased risk for measles compared with children who receive the vaccine at 1 year or older. Because specific groups were not at risk for vaccine failure, an immunization campaign targeting all school-aged children who lacks two doses of measles vaccine may be an effective measure to prevent outbreaks in Romania.