July 26, 2023

In The News: Maternal Vaccine Promising for Invasive Group B Strep in Infants

Medpage Today shares findings from a phase II study in South Africa that point to antibodies passing to infants when the vaccine is delivered during pregnancy. The hexavalent capsular polysaccharide cross (CPS)-reactive material glycoconjugate vaccine (GBS6) produced antibodies against group B streptococcus at IgG thresholds associated with reduced risk of invasive strep B disease in infants. Antibody responses were induced to all serotypes, with maternal-to-infant ratios between 0.4-1.3, depending on dosage.

A parallel sero-epidemiologic study was conducted in the same population and determined the IgG thresholds needed for a 75% to 95% reduction in the risk of disease. The percentage varied according to serotype and formulation, and had 57% to 97% of infants having a seroresponse to the most immunogenic formulation. The study authors noted no safety concerns for mothers or infants in their research.

The intrapartum antibiotic prophylaxis administered to pregnant women who test positive for group B streptococcus colonization in their third trimester has been more than 80% effective against early-onset disease in their infants. It has not, however, been shown effective against late-onset disease. The proposed maternal group B streptococcus vaccine, when given during pregnancy, could potentially prevent both early- and late-onset disease, according to the researchers. They also posit the vaccine could mitigate the need for the intrapartum antibiotic prophylaxis. This would be a benefit against antimicrobial resistance and disruption of the infant’s developing microbiome.

Most solicited systemic events were mild or moderate and similar between vaccine and placebo groups. There were three infant deaths in the vaccine groups and two in the placebo group, which were all deemed to be unrelated to the trial. For the mothers, unsolicited adverse events were in 45% to 70% of the vaccine groups and 61% for the placebo group.

PIDS member Carol Baker contributed an editorial comment regarding commercial apathy toward maternal vaccines that is included in the story. Dr. Baker said, “The protracted apathy was mitigated during the 2009 H1N1 influenza pandemic, when for the first time a substantial percentage of pregnant women received an influenza vaccine; then by the 2014 recommendation to give pregnant women a pertussis booster vaccine called Tdap to prevent death from pertussis in young infants; and finally during the coronavirus disease 2019 pandemic, when messenger RNA vaccines were recommended for pregnant women. At last, a maternal vaccine platform is moving toward widespread acceptance by women and their healthcare providers. The road to group B streptococcal vaccine licensure could occur through an accelerated pathway based on an established serologic correlate of protection followed by confirmation of effectiveness.”

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