WHO preferred product characteristics for group B streptococcus vaccines

Overview

Group B streptococcus (GBS) is a leading cause of sepsis and meningitis in neonates and young infants. It is also an important cause of stillbirth. GBS can be transmitted from the maternal ano-genital tract through mucosal surfaces to cause invasive disease in the foetus, newborn and young infant, potentially leading to stillbirth, early onset disease (<7 first days of life) and late onset disease (day 7 to first 3 months of life). Case fatality is high, particularly in early onset disease and resource poor settings. Maternal colonization in pregnancy has been found in a proportion of women (about 10–40%) in all geographical settings evaluated. Reported incidence of neonatal and infant invasive GBS disease varies geographically. The vast majority of the disease burden lies in low-and-middle-income>countries, with estimates as high as 3 cases per 1000 live births in some areas, excluding stillbirth. GBS is also a cause of invasive disease in women during and after pregnancy, and in the elderly, but precise disease burden estimates are lacking. Intra-partum antibiotic prophylaxis (IAP), based on pregnancy screening for GBS colonization or on the presence of other risk factors, has been only partially effective in reducing the risk of disease in high income countries, and is neither available nor practical in most resource-limited countries (1–4). IAP also raises concerns about emerging antimicrobial resistance and neonatal microbiome development.
 
Ten GBS envelope polysaccharide-based serotypes have been described, five of which (Ia, Ib, II, III, V) are estimated to account for the vast majority of the disease burden, although regional differences have been reported and more data are needed. Currently, no vaccine exists for prevention of GBS disease, but evidence suggests maternal immunization with protein-conjugated GBS capsular polysaccharides may reduce the disease risk in neonates and young infants in a serotype-specific manner through trans-placental passage of protective immunoglobulins (1, 5, 6). Protein-based vaccine candidates aiming to provide protection across the serotype spectrum are also under evaluation (7).

In its 2015 and 2016 meetings, the Product Development for Vaccines Advisory Committee (PDVAC), which informs SAGE on vaccine R&D matters and contributes to prioritize topics for WHO Initiative for Vaccine Research involvement, identified the development of GBS vaccines suitable for maternal immunization in pregnancy and use in low and middle income countries as a priority.