The US measles epidemics of 1989-1991 included a series of outbreaks resulting from vaccine failure. A series of studies was launched aimed at elucidating the mechanisms of this vaccine failure. A meta-analysis of the literature examining epidemics in vaccinated populations was conducted, which showed that the secondary vaccine failure rate (development of the disease despite an initial or primary vaccine success) is no more than 0.2%. The overwhelming proportion of measles vaccine failure was due to primary vaccine failure (failure to ever generate antibody from antigenic stimulation). This comparison of two geographically distinct communities revealed that 10% of children previously vaccinated against measles lacked antibody on follow-up and that these vaccine failures clustered in families. A study of monozygotic and dizygotic twins revealed a high degree of heritability of measles vaccine antibody level. Subsequent studies found associations with both class I and class II alleles in these population-based studies. In the future, detection of the specific peptides that interact with human leukocyte antigen (HLA) molecules may serve as the basis for improved vaccines and address vaccine failure that results from cold-chain problems, immaturity of the immune system, malnutrition and maternal immunity.