With Pfizer’s entry in the respiratory syncytial virus (RSV) race soaking up most of the press attention, it’s easy to forget that the Big Pharma has other vaccines in the works. They include a maternal vaccine for group B streptococcus (GBS), which has posted some positive data after a long period of radio silence.
Since Pfizer kicked off human trials for the GBS conjugate vaccine, dubbed GBS6, back in 2017, little has been heard about the candidate beyond securing breakthrough status from the FDA last year. But in a postmarket release Wednesday, July 19, the company published fresh phase 2 data for the vaccine in a journal that it said demonstrated “meaningful protection against invasive GBS disease in newborns and young infants.”
The data come from the second of a three-part study, which enrolled 360 healthy pregnant individuals in South Africa who received a dose of either 5, 10 or 20 µg/serotype. The findings from this cohort showed that GBS6 “generated robust maternal antibody responses” against the six GBS serotypes covered by the vaccine, Pfizer said.
These antibodies were efficiently transferred to infants at approximate ratios of between 0.4 and 1.3, dependent on the serotype. The highest antibody responses were generally observed with the 20-µg dose, the company noted.
The Big Pharma then compared these immunogenicity data to a parallel study of anti-CPS immunoglobulin antibody concentrations conducted in South Africa among 18,000 unvaccinated pregnant individuals and their infants, which suggested that GBS6 did offer protection. The safety profile in both mothers and infants was similar between the two studies, Pfizer noted, with most solicited systemic events classed as mild or moderate.
Depending on the dose received, between 45% and 70% of participants in the GBS6 trial experienced adverse events, compared to 61% of the placebo group. The most common adverse events and serious adverse events were conditions related to pregnancy, Pfizer added.
Among the infants, adverse events occurred in between 62% and 75% of the GBS6 groups and 74% of those in the placebo group. None of the serious adverse events were considered to be related to the vaccine, the company said.
As well as publishing the results in The New England Journal of Medicine, Pfizer said the data will now inform a phase 3 program. In the meantime, the final part of the phase 2 study will see a finalized formulation administered to 216 healthy pregnant individuals and their infants in South Africa, the U.S. and the U.K.
“Group B Streptococcus can cause potentially devastating diseases in infants, including sepsis, pneumonia and meningitis,” said Annaliesa Anderson, Ph.D., chief scientific officer of Pfizer’s vaccine R&D unit, in the release. “The findings published in NEJM provide hope that maternal vaccination with GBS6 may protect infants against GBS, potentially helping to prevent thousands of cases of illness annually, if it is successfully developed and approved.”
GBS, though mostly harmless in adults, poses a threat to young infants just weeks or months old as it causes sometimes lethal sepsis and meningitis. About one out of every four pregnant women carries GBS bacteria in her rectum or vagina. In developed countries, women who test positive for the bacteria receive intravenous antibiotics during labor to reduce the chances of passing it on to newborns. However, in countries without a robust health infrastructure, neither GBS screening nor routine administration of antibiotics is available.
The Bill & Melinda Gates Foundation awarded an undisclosed grant to Pfizer in 2016 to get the vaccine into phase 1/2 trials in South Africa, where GBS incidences were recorded at the time as being as high as 238 cases per 1 million live births. Last year, the foundation sent a further $128 million Pfizer’s way to fund both the GBS vaccine and its RSV program—which has since secured FDA approval.