Serotype specific anti-capsular polysaccharide IgG associated with colonizing and invasive group B streptococcus in pregnant woman-newborn dyads

In a Moroccan mother–newborn cohort, serotype IV anti-capsular polysaccharide IgG was sub-protective and linked to neonatal invasive GBS cases, despite predominant anti-serotype II immunity.

• Why it matters: Natural, serotype-specific anti-CPS immunity and its relationship to colonization versus invasive disease were not characterized in North African populations, limiting understanding of neonatal protection.
• What they did: Using a standardized six-plex immunoassay, investigators measured serotype-specific anti-CPS IgG (Ia–V) in maternal and cord plasma from 103 colonized women, 35 uncolonized controls, and 90 paired dyads, including five invasive cases.
• The result: Maternal IgG varied by serotype (highest median for serotype II at 1.36 g/mL; lowest for Ib at 0.003 g/mL), transfer was incomplete (median ratios 0.50–0.80), and 44.2% (n=34) of newborns met late-onset risk-reduction thresholds.

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