Seroprevalence and predictors of measles antibody positivity among children aged 18-24 months in Pakistan: a national survey.

BACKGROUND

Measles remain a leading cause of childhood morbidity and mortality. Despite improved vaccine coverage, the number of laboratory-confirmed measles cases in Pakistan doubled between 2019 and 2020. Although an effective vaccine has been available for decades, sporadic outbreaks continue to occur. This study aimed to determine the seroprevalence of measles IgG antibodies among vaccinated children in Pakistan.

METHODS

A cross-sectional survey was conducted between April 2019 and October 2020 in seven districts across Pakistan. Using a multistage sampling technique, healthy children aged 18-24 months with a history of measles vaccination were randomly enrolled after obtaining informed written consent. Venous blood samples (3 cc) were collected and tested for measles IgG antibodies using ELISA.

RESULTS

Among 3596 vaccinated children, 65% were seropositive for measles IgG antibodies. Vaccine coverage was high, with 90% receiving the first measles dose (MCV1) administered at 9 months of age and 78% the second dose (MCV2) administered at 15 months. Seropositivity was significantly associated with vaccination source, documentation status, rural residence, place of delivery, and history of prior measles infection. Higher seroprevalence was observed among children vaccinated by mobile vaccinators compared to other vaccination settings.

CONCLUSION

Seroconversion among vaccinated children was suboptimal, with only 65% achieving protective antibody levels. The first dose of measles vaccine appeared particularly important for antibody development. Strengthening vaccination services, ensuring delivery through trained vaccinators, and conducting regular seroprevalence surveys are essential for evidence-based policies to achieve measles elimination in Pakistan.