Objective: Measles, rubella, mumps, and varicella are currently endemic in Vietnam, but population immunity to the four diseases among the general population has not been well investigated. This study measured specific immunoglobulin (Ig)G in 362 randomly selected adults between 20 and 70 years old, using residual serum samples to evaluate age-specific immunity to the four diseases in Khanh Hoa province.
Results: Age-specific anti-measles IgG prevalence was lowest, at 89.3% (95% confidence interval 71.8–97.7%) at 20–24 years old, below the herd immunity threshold of 95% to prevent epidemics. About 71.4–90.3% of women of child-bearing age (20–49 years old) were seropositive for rubella, indicating that a certain proportion of babies are at risk of congenital rubella syndrome. A large proportion of young adults (20–29 years) are susceptible to mumps and varicella, with population immunity of 71.4–78.1% to mumps and 48.8–53.6% to varicella. Population-based seroprevalence surveys of both children and adults are needed to evaluate population immunity and improve current immunization programs by expanding the target ages for immunization and introducing new vaccines.