Pfizer announced in September 2022 that its investigational Group B Streptococcus (GBS) vaccine candidate, GBS6, or PF-06760805, had received Breakthrough Therapy Designation from the FDA. The vaccine is intended for the “prevention of invasive GBS disease…by active immunisation of their mothers during pregnancy”.  

The decision comes amidst an ongoing study, evaluating the safety and immunogenicity of GBS6 in healthy pregnant women between the ages of 18 and 40, who received vaccination during their second or early third trimesters. This is a placebo-controlled Phase II study, NCT03765073.  

What is GBS? 

GBS is a bacterium that causes “potentially devastating diseases in infants”, such as sepsis, pneumonia, and meningitis during the first 3 months of life. Pfizer stated that “about 1 in 4 pregnant women carry GBS bacteria in their body” with the potential to pass it on to their infant “during or prior to birth”. The annual global burden is an estimated 410,000 cases worldwide, with more than 147,000 stillbirths and infant deaths.  

Breakthrough Therapy Designation 

The FDA’s Breakthrough Therapy Designation is “designed to expedite the development and review” of vaccines that are considered better than current therapies. In order to obtain this status, preliminary clinical evidence must demonstrate “substantial improvement” on “clinically significant endpoints”. The attainment of this status follows the FDA’s decision to grant Fast Track status to GBS6 in March 2017.  


The vaccine candidate is designed to offer protection against the “6 most prominent GBS serotypes”, which comprise 98% of the disease. The vaccine is an investigational maternal vaccine, hexavalent anti capsular polysaccharide (CPS)/cross reactive material 197 glycoconjugate.  

It is undergoing evaluation in a Phase II study across South Africa, the UK, and the US. In April 2022 GBS6 was granted PRIME designation by the EMA’s Committee for Medicinal Products for Human Use (CHMP). This “provides enhanced support for the development of medicines that target an unmet clinical need”. In 2016 Pfizer reported receiving a grant from the Bill and Melinda Gates Foundation towards the ongoing clinical trial and a “parallel non-interventional natural history study”.  

Dr Annaliesa Anderson, Senior Vice President and Head of Vaccine Research and Development at Pfizer, stated that GBS infections have “devastating” effects on new-borns and their families. Although she credits prenatal screening and antibiotics during childbirth with providing protection against GBS, she is concerned that this approach is not “fully protective in the first week of life”. Furthermore, it “presents multiple challenges in low- and middle-income countries” and “has not been shown effective” up to the first 3 months of life.  

“If approved for pregnant women, GBS6 could help protect new-borns from the serious illnesses caused by this disease like meningitis, pneumonia, and sepsis”. 

Dr Anderson is “encouraged” by the FDA’s decision and is prepared to discuss the vaccine candidate with the FDA and other agencies to “potentially reduce neonatal deaths” as well as the “global disease burden of GBS”.

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