The use of IgM tests for analysis of the causes of measles vaccine failures: experience gained in an epidemic in Hungary in 1980 and 1981.

Following a period of 6 years of low measles incidence, an epidemic occurred in Hungary with more than 11,000 reported cases between September 1980 and August 1981. About 60% of the cases had a documented history of previous measles vaccination. Serum samples obtained from 7815 patients were examined for measles antibody by haemagglutination inhibition (HI). In addition to conventional antibody titration, most of the sera or their IgM fraction obtained by a simple ion exchange chromatography were tested for the presence of measles-specific IgM antibodies by 2-mercaptoethanol (2-ME) treatment, and in 300 patients also by the fluorescent antibody (FA) technique. Laboratory results confirmed the diagnosis of measles in 5356 patients and supported it in 685 cases. Primary antibody response was found in 96.1% of unvaccinated and in 77.4% of previously vaccinated patients. The percentage of secondary antibody responses increased with increasing time from vaccination only in patients vaccinated before their first birthday, whereas in those who were immunized when over 12 months old, the distribution of primary and secondary antibody responses was independent from the time that had elapsed since vaccination. Therefore, secondary vaccine failure due to waning immunity account for only 6.2% of previously vaccinated patients, whereas in 93.8% of patients, including the majority of those with secondary antibody response, a primary failure of vaccination due to unsuccessful immunization was incriminated.