Measles seroprevalence in pregnant women in Soweto, South Africa: a nested cohort study

Objectives: Measles infection causes particularly severe disease in young children who, prior to vaccination, are dependent on maternal antibodies for protection against infection. Measles vaccination was introduced into the South African public immunization programme in 1983 and became widely available in 1992. The aim of this study was to determine measles-specific immunoglobulin G (IgG) levels in pregnant women living with and without HIV born before and after measles vaccine introduction in South Africa. Methods: Measles IgG antibody level from blood obtained at the time of delivery was compared between women who were born before 1983 (n = 349) and since 1992 (n = 349). Serum samples were tested for measles IgG antibody using an enzyme-linked immunosorbent assay. Geometric mean titres (GMTs) and the proportion with seronegative (<200 mIU/mL) or seropositive titres (≥275 mIU/mL) were compared. Results: Women born since 1992 had lower GMTs [379.7 mIU/mL (95% CI 352.7–448.6)] and fewer were seropositive (55.9%, 195/349) than women born before 1983 [905.8 mIU/mL (95% CI 784.7–1045.5); 76.8%, 268/349], for both comparisons p < 0.001. Conclusions: We found an association between measles vaccine implementation into the public immunization program in South Africa and peri-partum maternal measles immunity, where women born before vaccine introduction had higher measles IgG antibody titres and were more likely to be seropositive. These findings suggest a need to reconsider the infant measles immunization schedule in settings where women have derived immunity mainly from measles vaccine rather than wild-type virus exposure.