A laboratory study released on Wednesday suggested that the South African virus variant may reduce protective antibodies elicited by the Pfizer/BioNTech vaccine by two-thirds, but it is not clear how much that reduces the shot's effectiveness against this version of the pathogen.
Phil Dormitzer, one of Pfizer's top viral vaccine scientists and a co-author of the study, said in an interview he believes the current vaccine is highly likely to still protect against the concerning variant first discovered in South Africa.
"A level of neutralizing antibodies that may be on the order of between a third and a half the level of neutralizing antibodies you see against the original virus does not mean you have only a third to half of the protection level, you may well have full protection," he said.
University of Texas Medical Branch professor and study co-author Pei-Yong Shi said he also believes the lessened immune response observed is likely to be significantly above where it needs to be to provide protection.
Shi said that in clinical trials, both the Pfizer/BioNTech vaccine and a similar shot from Moderna Inc conferred some protection after the first of two doses with an antibody response lower than the reduced levels seen in the laboratory study of the South African variant.
Still, Dormitzer, chief scientific officer of viral vaccines at Pfizer Vaccines Research and Development, said the company was developing plans to test a redesigned booster for the vaccine.
"We're not doing that primarily because we think that means that we're going to need to change that vaccine," he said. "It's primarily to learn how to change strain, both in terms of what we do at the manufacturing level, and especially what the clinical results are.
"So if a variant comes along for which there is clinical evidence of escape, we're ready to respond very quickly," Dormitzer added.
He said the company has already made a DNA template for a prototype vaccine targeting the variant and plans to manufacture a batch of it.
The company is proposing to do a Phase I clinical trial of a booster shot of that prototype vaccine that it would test against a booster for the current vaccine.
"This will be a immunogenicity study where you look at the immune response. And those studies are much, much smaller than the giant efficacy studies," Dormitzer said.
"In immunogenicity studies you can look at the immune response of every person in the study. It's not as definitive as efficacy data, for sure. But it can be gathered much more quickly," he explained.
The company would likely conduct some animal testing in parallel as well, he said.
The US Food and Drug Administration has not yet released a roadmap for how companies should design trials of coronavirus booster shots.