Measles outbreak after a post-honeymoon period in Mongolia, 2001.

In spite of the routine 2-dose vaccination and three recent supplemental immunizations, Mongolia experienced a measles outbreak in 2001, the largest epidemic in the country since 1984. The majority of cases were reported in the capital city, and the disease incidence was higher in infants and adolescents than in other age groups. Young adults who received the immunization only once may have low immunity, and may be exposed to the virus most frequently. Immunization strategies such as the age range that is targeted for vaccination and the interval between supplemental immunizations should be based on reasonable epidemiological observations.