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

A measles epidemic occurred in Romania with 32,915 cases and 21 deaths repo rted 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 evalua te age at Vaccination and waning immunity as risk factors for vaccine failu re. Both studies indicated that measles vaccine was highly effective. One d ose reduced the risk for measles by 89% (95% confidence interval (CI) 85, 9 1); two doses reduced the risk by 96% (95% CI 92, 98). Children vaccinated at cl year of age were not at increased risk for measles compared with chil dren vaccinated at greater than or equal to 1 year. Waning immunity was not identified as a risk factor since Vaccine effectiveness was similar for ch ildren 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 str ategy 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.