In the Journals: Evaluating a Vaccine Against Group B Streptococcus

Group B Streptococcus (GBS) is a common cause of sepsis and meningitis in newborns through the first three months of life. In the United States, and many other high-income countries, pregnant women undergo screening for colonization with GBS in the third trimester; prophylactic antibiotics are administered to those with positive results. While intrapartum antibiotics are about 80% effective in preventing early-onset GBS infection (i.e., 0-6 days of age), they have been ineffective at preventing late-onset disease (i.e., 7-89 days of age). Therefore, a maternal GBS vaccine, which could result in passively transferred antibodies that are effective for as long as four to six months, would be of value.

Researchers at Pfizer evaluated the ability of a single-dose maternal GBS vaccine to induce levels of anti-GBS capsular polysaccharide (CPS) antibodies likely to be associated with protection against disease (Madhi SA, Anderson AS, Absalon J, et al. Potential for Maternally Administered Vaccine for Infant Group B Streptococcus. N Engl J Med. Jul 20; 2023;389(3):215-227). The level of anti-capsular antibodies likely to be associated with protection was based on previous natural history studies of GBS-infected infants. The vaccine, which was called GBS6, contained six of the 10 GBS capsular polysaccharides that cause 98% of cases of invasive GBS disease worldwide. The capsular polysaccharides from these six GBS serotypes were linked to a genetically modified non-toxic form of diphtheria toxin. Researchers evaluated 5 micrograms (ug), 10ug and 20ug doses in vaccine formulations that either did or did not contain an aluminum phosphate adjuvant. They found that 57% to 97% of infants had a protective antibody response to the most immunogenic formulation.

The authors concluded, “GBS6 elicited anti-CPS antibodies against group B streptococcus in pregnant women that were transferred to infants at levels associated with a reduced risk of invasive group B streptococcal disease.” (abstract)