Amid the complexities of conducting an efficacy study for a group B streptococcus (GBS) vaccine, Pfizer’s lead vaccine executive is advocating for regulatory approval based on an immunogenicity study, similar to the approach taken for the company’s meningitis B and pneumococcal vaccines.
Given the relatively low incidence rates of GBS, Pfizer is crafting a phase 3 study design centered on assessing antibody transfer from mother to baby and the vaccine’s impact.
While the precise market potential for Pfizer’s GBS vaccine remains uncertain, Anderson emphasized the goal of securing approval in major markets, particularly the US and Europe. Notably, disease prevention measures and screening have substantially reduced GBS cases in the US, dropping from 1.7 cases per 1,000 live births in 1993 to 0.2 cases per 1,000 live births in 2020, as per CDC data. However, these measures have been less effective against infections in infants older than one week.
The GBS bacterial infection can lead to severe conditions like meningitis and bloodstream infections, with fatality rates of 4-6% among affected babies.
Pfizer’s phase 3 plans follow midstage results unveiled in July, indicating that the vaccine induced antibody production in pregnant individuals, with successful transfer to their infants. The antibody transfer ratio ranged from 0.4 to 1.7 based on the serotype. The trial enrolled 360 healthy pregnant participants who received varying vaccine doses, comparing the findings to a parallel natural history study involving 18,000 pregnant individuals. Adverse event rates were comparable between the vaccine and placebo groups.
Backing Pfizer’s ongoing clinical development are grants from the Bill & Melinda Gates Foundation, including a $100 million contribution earmarked for phase 3 development granted in May 2022. This funding will also aid in expanding vaccine access in lower-income countries.
