Streptococcus agalactiae bacteria responsible for vaginal, urinary and neonatal infections, including meningitis and septicemia. Optical microscope view.
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Pfizer announced on Wednesday that its experimental vaccine against the potentially deadly bacterial disease group B streptococci has delivered strong results in mid-stage clinical trials, a promising step towards potential approval of the drug.
Pfizer is one of several drugmakers battling to develop the world’s first vaccine against group B streptococcus, which is linked to nearly 150,000 infant deaths worldwide each year, particularly in low-income countries.
The Food and Drug Administration granted Pfizer’s vaccine Breakthrough Therapy designation in September, which should speed up the development and testing of the vaccine.
Pfizer’s single-dose syringe produced antibodies that could offer infants effective protection against the disease, according to data from a phase 2 clinical trial released Wednesday.
The vaccine is given to expectant mothers, who pass vaccine-induced antibodies to their fetuses. One of the company’s respiratory syncytial virus vaccines also uses this maternal vaccination method.
The encouraging results from Pfizer’s Phase 2 trial raise hopes that vaccinating mothers against the disease, also known as GBS, could help prevent thousands of cases in babies.
The results will also help the company plan its Phase 3 clinical trials of the vaccine, which are typically required before the FDA approves a drug.
The Bill & Melinda Gates Foundation, which supported the Phase 2 trial, provided Pfizer with an additional $100 million grant last year to fund late-stage trials and help increase vaccine delivery to facilitate lower-income countries after possible admission.
GBS disease is caused by a common and usually harmless bacterium that many adults carry in their bodies.
But an expectant mother can transmit these bacteria to her newborn during labor and delivery, which can lead to serious infections in the baby’s first few weeks or months.
About one in four women carries GBS bacteria, according to the Centers for Disease Control and Prevention.
Infants with GBS infections may experience symptoms such as fever and difficulty breathing.
Some infants can develop invasive GBS infections, causing more serious complications such as pneumonia, bloodstream infections, and meningitis, or inflammation of the tissues around the brain and spinal cord.
There are 10 different GBS serotypes, which are different variations of the bacteria that cause the disease. Pfizer’s vaccine targets six of the most well-known serotypes, which together account for 98% of GBS cases worldwide.
Test Results and Safety
The Pfizer study followed 360 healthy pregnant women in South Africa. The mothers were randomly assigned a single syringe of three different doses, with or without a specific adjuvant, or a placebo.
The study found that Pfizer’s vaccination produced robust antibodies against the six GBS serotypes in mothers. These antibodies were “efficiently” delivered to infants at ratios of between 0.4 and 1.3, depending on the dose.
This means that some infants received only a fraction of the antibodies from their mothers, while others received higher levels of antibodies than even their mothers.
Pfizer said these antibody transmission levels were linked to a reduced risk of GBS disease. This conclusion was based on a parallel natural history conducted in South Africa.
According to the study results, the safety profile for mothers and infants appeared to be similar between the vaccine and placebo groups, indicating that the vaccine was generally well tolerated during the Phase 2 study.
Maternal reactions after vaccination were generally mild to moderate and of short duration. According to the results, between 2 and 8 percent of participants who received the vaccine reported a fever, compared with 5 percent in the placebo group.
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About 45 to 70% of pregnant people who received the vaccine experienced more side effects such as headaches and vomiting. But it was not much different in the placebo group: more than 60% of the expectant mothers experienced these adverse events.
About 62% to 75% of infants in the vaccine group and 74% of infants in the placebo group experienced adverse events, including upper respiratory tract infection. There were three infant deaths in the vaccine group and two in the placebo group.
The study authors noted that no adverse events or deaths in infants were related to the vaccine.
The results come as Pfizer braces for a prolonged decline in Covid-related sales this year.
Pfizer also faces a patent cliff, or loss of market exclusivity, for several blockbuster drugs like cancer drugs Xtandi and Ibrance. This is expected to further hurt Pfizer’s annual sales through 2030.
To counteract a sharp decline in sales, the company is shifting its focus to a new drug pipeline and M&A.