Measles seroepidemiology and risk factors for low seroprevalence among newborns and children in Nha Trang, Viet Nam

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Background: Despite high reported routine vaccination coverage at 9 and 18 months, measles outbreaks occur every 3–5 years in Viet Nam, as in other low- and middle-income countries. However, measles seroepidemiology and risk factors for low seroprevalence among children remain unclear. Methods: We conducted two cross-sectional studies on newborns and pediatric cases aged 1 month to 5 years using stored samples and information from a birth cohort study (July 2017–September 2018), and surveillance for childhood acute respiratory infections (September 2017–August 2022) in Nha Trang, respectively. We assessed age-specific measles seroprevalence by enzyme immunoassay for anti-measles IgG antibodies and the associations with their characteristics using logistic regression. Results: Of 1008 newborns, seroprevalence was 83.7%. We found lower measles seroprevalence in cord blood from mothers aged ≤24 years, compared with those aged ≥35 years (adjusted OR [95% CI]: 0.11 [0.04–0.26]), and from mothers in suburban communes (0.67 [0.47–0.96]). Among 1547 pediatric cases, seroprevalence was 43.0%, 68.0%, and 77.9% for those aged 1–<9 months, 9–<18 months, and ≥ 18 months, respectively, with the lowest seroprevalence of 26.0% at 8 months. We found lower measles seroprevalence among cases aged <9 months and 9–<18 months (adjusted OR [95% CI]: 0.43 [0.27–0.69] and 0.62 [0.43–0.89], respectively, compared with those aged ≥18 months), those in households with ≥4 members (0.62 [0.42–0.91]), and those without measles vaccination history (0.35 [0.26–0.48]). Conclusions: Risk-based interventions, particularly early measles vaccination, should be considered for protecting vulnerable children from measles.