Pfizer kicks off human testing with maternal GBS vaccine

Though blockbuster Prevnar 13 is still the backbone of Pfizer’s vaccine portfolio, its slowing sales have increased pressure on the drug giant to explore other opportunities, and a vaccine against Group B streptococcus (GBS) is among those efforts.

Pfizer announced on Monday it started a phase 1/2 trial of its GBS conjugate vaccine dubbed PF-06760805, which incorporates at least five serotypes of GBS and could prevent approximately 95% of GBS disease in infants via maternal immunization, according to a company spokesperson.

“We are looking to determine whether our investigational vaccine could generate levels of protective antibodies in the mother that, when passed to her unborn baby, will protect the baby against deadly GBS infection during a time when the infant is most vulnerable to infection,” a company spokesperson told FiercePharma.

Researchers will enroll 363 healthy U.S. women aged 18 to 49 who have no history of GBS infection. The participants will be divided into seven groups, six of which will get the vaccine in either of two formulations in one of the three doses; the rest will receive placebo, according to The plan is to evaluate safety, tolerability and immunogenicity by May 2018.

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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 1 out of every 4 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.

Besides the U.S. trial, Pfizer nabbed an undisclosed amount of grant from the Bill & Melinda Gates Foundation last October to help test the candidate in a phase 1/2 clinical trial in South Africa, where GBS incidences are as high as 238 cases per 1 million live births. The trial is projected to start in 2019, and Pfizer is determining the exact number of trial sites and participants, according to the spokesperson.

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The company's new study comes during a damaging sales slide for Pfizer’s star vaccine Prevnar 13. Last year, sales for the vaccine fell 8% to $5.7 billion due to what the company called high initial uptake, meaning fewer eligible patients remain. Since Pfizer has done so well with that conjugate vaccine against pneumococcus, it’s possible the drugmaker could find new success in one against GBS, which also belongs to the streptococcus family. However, the field is not without competition.

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GlaxoSmithKline is currently leading with a trivalent candidate it got from Novartis during the 2015 vaccine-oncology asset swap. According to a study published in Lancet Infectious Diseases last April, in a phase 1b/2 single-center study in South Africa on 60 non-pregnant and 320 pregnant women, the vaccine was well tolerated and induced capsular-specific antibody responses, and led to higher GBS antibody concentrations in infants than did the placebo. Several multicenter phase 2 studies have also been completed by Novartis and GSK in developed countries like the U.S.

Pfizer is certainly not putting all eggs in one basket, though. Its Meningococcal group B vaccine Trumenba just won an EU approval to go against GSK’s rising star Bexsero, whose sales more than doubled to reach £390 million ($500 million) in 2016. Others in its pipeline include a shot against C. difficile, chasing Sanofi Pasteur in phase 3; an FDA-fast-tracked four-antigen S. aureus vaccine in phase 2, and two vaccines in phase 1 targeting bacterial infections and prostate cancer separately.