Abstract
Group B Streptococcus serotype-specific IgG immunity in mother-newborn dyads in South Asian and African countries: a multicountry study, 2016-2018
Kwatra, G.
Izu, A.
Mukendi, C.
Dhar, N.
Ali, M. M.
Akaba, G.
Ahmed, Z.
Beck, M. M.
Barsosio, H. C.
Berkley, J. A.
Chaka, T. E.
Cossa, A.
Chakraborty, S. R.
Cutland, C. L.
Dorji, P.
Islam, M.
Keita, A. M.
Mwakio, S.
Mwarumba, S.
Medugu, N.
Lema, F. B.
Obaro, S.
Olateju, E. K.
Sigaúque, B.
Sow, S. O.
Saha, S. K.
Santhanam, S.
Sharma, R.
Simões, E. A. F.
Sahni, R. D.
Tapia, M. D.
Veeraraghavan, B.
Madhi, S. A.
Clin Microbiol Infect. 2026;
Permanent descriptor
https://doi.org/10.1016/j.cmi.2026.09.032OBJECTIVE: To evaluate sero-epidemiology of maternal and cord blood Group B Streptococcus (GBS) serotype-specific capsular polysaccharide (CPS) IgG concentrations and transplacental antibody transfer across diverse low middle-income country populations. METHODS: We conducted a multicountry, cross-sectional study among pregnant women without human immunodeficiency virus (HIV) infection and their newborns across six African (South Africa, Kenya, Mozambique, Ethiopia, Mali and Nigeria) and three South Asian countries (Bhutan, Bangladesh and India). Maternal and cord blood samples were collected at delivery and analysed using a multiplex immunoassay for serotype-specific CPS GBS IgG. RESULTS: We analysed 2293 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 geometric mean ratios (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 varied widely across countries ranging from 10.0% to 56.8% for serotype Ia and 13.5% to 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.