Group B Streptococcus serotype-specific IgG immunity in mother-newborn dyads in South Asian and African countries: a multicountry study, 2016-2018.

OBJECTIVE

To evaluate the sero-epidemiology of maternal and cord blood Group B Streptococcus (GBS) serotype-specific capsular polysaccharide (CPS) immunoglobulin G (IgG) concentrations and transplacental antibody transfer across diverse low-middle income country populations.

METHODS

We conducted a multi-country, cross-sectional study among pregnant women without HIV-1 infection and their newborns across six African (South Africa, Kenya, Mozambique, Ethiopia, Mali, Nigeria) and three South Asian countries (Bhutan, Bangladesh, India). Maternal and cord blood samples were collected at delivery and analyzed using a multiplex immunoassay for serotype-specific CPS GBS IgG.

RESULTS

We analyzed 2,293 mother-newborn dyads. Maternal serotype-specific CPS-IgG concentrations varied significantly by country and serotype. Most women had detectable serotype-specific IgG antibodies, with >95% of participants having detectable antibodies against serotypes II, III, and IV across most countries, whereas lower proportions were observed for serotypes Ib and V. Serotype II demonstrated the most efficient transplacental transfer ratios with GMRs ranging from 0.80 (95% CI 0.74-0.85) in South Africa to 1.16 (95% CI 1.07-1.27) in Bhutan. Transfer was generally lower for other serotypes, particularly in Kenya, where GMRs ranged from 0.51 (95% CI 0.46-0.58) for serotype IV to 0.81 (95% CI 0.73-0.91) for serotype II. The proportions of newborns above the serotype-specific serological thresholds of risk reduction (SToRR) varied widely across countries ranging from 10.0%-56.8% for serotype Ia and 13.5%-68.0% for serotype III. Bangladesh consistently had the highest maternal and cord blood antibody concentrations whereas Bhutan and Ethiopia had the lowest.

CONCLUSIONS

Marked geographic and serotype-specific variability in maternal and neonatal GBS IgG concentration was observed across South Asian and African countries. These findings provide important information on baseline naturally acquired immunity and transplacental antibody transfer, which may inform the evaluation and implementation of maternal GBS vaccines in diverse populations.