Peer-reviewed article
Strengthening measles immunity in Thailand: Rationale for a third vaccine dose to avert outbreaks.
Pornjarim Nilyanimit, Nungruthai Suntronwong, Jiratchaya Puenpa, Thanunrat Thongmee, Sirapa Klinfueng et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001A study of measles immunity in Thailand found that only 61% of the population has protective antibody levels, far below the 92% threshold needed to stop disease transmission. Young people aged 14 to 31 years are particularly vulnerable, with only 27–46% having adequate immunity despite receiving two vaccine doses. The research suggests a third measles vaccine dose for adolescents and adults aged 10 to 40 years could close immunity gaps and help Thailand achieve measles elimination.
Key points
- Overall seropositivity in 2024 was 61.3%, well below the 92% herd immunity threshold needed to interrupt measles transmission
- Adolescents and young adults aged 14–31 years had low immunity (27–46%), despite national immunization programs
- Adults over 40 years showed high seroprotection (>95%) from natural infection, while vaccine-era cohorts born 1985–2008 showed progressive immunity decline
- Most measles cases in 2024 occurred in individuals older than 15 years, reflecting the identified susceptibility pattern
- Authors recommend a third measles-containing vaccine dose for ages 10–40 years, integrated into adolescent or adult booster programs
Limitations
This is a cross-sectional serosurvey describing immunity levels and does not evaluate the effectiveness of any intervention to improve them. The study cannot directly demonstrate that a third dose would prevent outbreaks or determine optimal delivery strategies.
Abstract
Achieving measles elimination in Thailand requires restoring population immunity to levels sufficient to interrupt transmission. Recent outbreaks indicate widening immunity gaps despite long-standing national immunization programs. We assessed measles-specific immunity using 3675 age-representative serum samples collected in 2024 from four provinces. IgG concentrations were measured by ELISA with a protective threshold of ≥200 IU/L and interpreted alongside national serosurveys conducted in 2004 and 2014 to evaluate temporal changes in immunity across vaccine-era birth cohorts. Overall seropositivity in 2024 was 61.3% and showed a pronounced U-shaped age pattern. Adults older than 40 years had high seroprotection above 95% consistent with natural infection. Adolescents and young adults aged 14 to 31 years had much lower immunity ranging from 27% to 46%. Birth-cohort analysis revealed progressive declines in seroprotection among individuals born between 1985 and 2008, indicating low seroprevalence of vaccine-induced immunity. National case data from 2024 reflected these findings, with most infections outside deep southern provinces occurring in individuals older than 15 years. Thailand's current immunity levels fall below the herd immunity threshold needed to halt measles transmission, estimated at 92% or higher. The high susceptibility in adolescents and adults suggests that two routine doses are inadequate under current epidemiologic conditions. These results suggest the findings warrant further evaluation of targeted booster strategies, including potential role of a third measles-containing vaccine dose for individuals aged 10 to 40 years. Integrating this dose into adolescent or adult booster programs, along with strengthened surveillance and targeted catch-up vaccination in low-coverage regions, offers a practical pathway to closing immunity gaps and accelerating progress toward measles elimination.