Measles sero-surveillance during mass immunisation campaign in Malawi

Objective: To determine age-specific measles antibody prevalence and serological response to vaccination during the first mass campaign against measles in Malawi. Design: Cross-sectional study using a questionnaire and a serological particle agglutination (PA) test. Setting: Two health centres in Salima district, central Malawi during the national measles immunisation week, 1998. Participants: Two hundred forty six under-five year old children. Results: Seventy four per cent of enrolled children (95% confidence interval, 69-80%) were measles PA antibody positive at the vaccination. The antibody positive rate was 17.4% in children aged 8-12 months and gradually increased up to 90% by four years-old, while the age-specific geometric mean titers (GMTs) in 48-59 months-old group were significantly lower than those in 24-35 months-old group, suggesting antibody waning after previous vaccination (p=0.0047). Two hundred and thirty follow up specimens were obtained eight weeks after the vaccination. The sero-conversion rate was 100% in 58 children sero-negative at the vaccination and the GMTs in 172 children seropositive at the vaccination were significantly increased (p<0.001). Conclusion: These results indicated that the first national measles immunisation campaign successfully immunised the enrolled children or gave a booster response of antibody levels. It was also confirmed that the PA test was easy to perform and most suitable for the field condition in developing countries.