Pfizer and BioNTech are beginning a large study of a candidate vaccine for Covid-19 with the goal of obtaining approvals, but it’s not the one for which results were released earlier this month.
The companies have always said they planned to choose from four different candidates, all of whom use a technology called messenger RNA to make a protein in SARS-CoV-2, the virus that causes Covid-19. The vaccine is designed to make the immune system recognize the protein and is expected to attack the virus.
On July 1, the companies announced results in a pre-print publication showing that a vaccine candidate, BNT162b1, elicited an immune response in patients. That vaccine encoded a key portion of the spike protein, which SARS-CoV-2 uses to enter cells. The vaccine being carried out, BNT162b2, encodes an optimized version of the entire spike protein, which should lead to “more consistent responses in various populations and in older adults,” Pfizer said in a statement.
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Philip Dormitzer, Pfizer’s vice president in charge of vaccines, said the selected vaccine appears to elicit a stronger response, in part because it includes more of the spike protein. That could mean less variability in how people respond to the vaccine. It also seemed to cause fewer side effects. “It seemed a little softer,” Dormitzer said in an interview. “There were fewer reactions to immunization, and that was an important mark in his favor.”
It is unclear why this candidate vaccine would have milder side effects, but Pfizer scientists speculate that it is due to changes in messenger RNA that facilitate the production of mammalian cells. Whatever the reason, Dormitzer said, this is the candidate Pfizer is testing during the pandemic, although he cannot rule out that other variants may be withdrawn from the market in the future. “This is really the final choice,” he said.
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The study, which began today, will recruit about 30,000 healthy volunteers between 18 and 85, randomizing half to receive the vaccine and the rest to receive placebo. Pfizer will recruit from approximately 120 sites in countries around the world, including the US, Germany, and Brazil. The primary goal is to prevent patients from developing Covid-19, and secondary endpoints include preventing severe cases of the disease and protecting volunteers from asymptomatic infections.
The announcement came hours after Moderna began its own test of 30,000 participants. Like Pfizer and BioNTech, Moderna’s vaccine uses messenger RNA to force the body to produce spike proteins, leading to an immune response that will ideally protect Covid-19 subjects.
Pfizer and BioNTech said they are on track to request a regulatory review in early October, and that they plan to supply up to 100 million doses by the end of 2020 and 1.3 billion doses by the end of 2021.
