Seroprevalence of Measles IgG Antibodies in Bahrain: A Cross-Sectional Study Using Fever and Rash Surveillance Data (2021–2025)

• A seroprevalence study nested in Bahrain’s fever and rash surveillance system. • Age-adjusted measles IgG seroprevalence was 94.3% (95% CI 85.7–97.9). • Seroprevalence was 10.5% under 6 months and 4.9% at 6–12 months of age. • Non-Bahraini patients had lower measles IgG seroprevalence than Bahrainis. • Two-dose measles vaccine recipients reached 99.6% IgG seropositivity. Measles remains a public health challenge despite effective vaccines; recent declines in coverage led to resurgent outbreaks worldwide. This study aims to estimate measles IgG seroprevalence in Bahrain’s population and identify immunity gaps using serological data from the national fever and rash surveillance system. We analyzed fever and rash surveillance data from Bahrain (2021–2025). Suspected measles cases were tested for measles IgG antibodies. Seroprevalence was stratified by age, nationality, vaccination status, and governorate. Overall prevalence was age adjusted, and differences in seropositivity were tested using chi-square tests. Among 1,280 patients, the overall seroprevalence of measles IgG was 81.6% (95% CI: 79.3%–83.7%). Seropositivity differed between Bahrainis and non-Bahrainis (82.6% vs 77.3%; p-value = 0.047). There was strong evidence of differences in seroprevalence by age (p-value < 0.001). Seroprevalence was 10.5% among those less than 6 months and dropped to 4.9% among those aged 6 to 12 months. Adjusted for age, seroprevalence was 94.3% (95% CI 85.7%–97.9%). Bahrain’s age adjusted measles seroprevalence is within herd immunity thresholds. However, vulnerabilities exist among those aged less than 18 months and non-Bahrainis. Sustained high MMR vaccine coverage and enhanced surveillance are important in maintaining measles elimination status.