Abstract
Thailand's Expanded Program on Immunization revised the timing of the second measles, mumps, and rubella (MMR) vaccine dose to 2.5 years in 2014 and later to 1.5 years in 2020. These adjustments can temporarily reduce vaccine coverage as the population transitions to the new schedules. Combined with disruptions caused by the coronavirus disease 2019 (COVID-19) pandemic, these changes may have adversely affected vaccine uptake and overall population immunity. This study aimed to evaluate the age-specific seroprevalence of anti-measles, anti-mumps, and anti-rubella IgG in individuals across all age groups in Chonburi province, Thailand, following the COVID-19 pandemic. Between October 2022 and January 2023, 650 participants from Chonburi were included and categorized into nine age groups: <5, 5-10, 11-20, 21-30, 31-40, 41-50, 51-60, 61-70, and >70 years. The levels of antibodies were analyzed using commercial ELISA kits. Overall, 77.5%, 55.1%, and 84.1% were seropositive for MMR antibodies, respectively. Adolescents aged 11-20 years had the lowest seropositivity rates for measles (47.0%) and mumps (27.6%), followed by young adults aged 21-30 years. Rubella seropositivity rates were similarly low in these groups. This study highlights immunity gaps for measles in adolescents and young adults. To address this gap and support ongoing measles elimination efforts, targeted interventions, such as supplementary immunization activities with a booster dose of measles-containing vaccines for this age group, are recommended to prevent the potential resurgence of measles in the near future.