Pfizer says variant identified in South Africa could result in fewer protective antibodies
Study found mRNA vaccine was still able to neutralize virus but booster shot may be needed
A top Pfizer scientist says the company is in intensive discussions with regulators to test a booster shot version of its coronavirus vaccine specifically targeted for a highly contagious variant that is spreading widely in South Africa and elsewhere.
A laboratory study released on Wednesday suggested that the coronavirus variant first discovered in South Africa 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 on Thursday that 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.
Reduction in antibodies
For the study, scientists from the companies and the University of Texas Medical Branch (UTMB) developed an engineered virus that contained the same mutations carried on the spike portion of the highly contagious coronavirus variant first discovered in South Africa, known as B1351.
The spike, used by the virus to enter human cells, is the primary target of many COVID-19 vaccines.
Researchers tested the engineered virus against blood taken from people who had been given the vaccine, and found a two-thirds reduction in the level of neutralizing antibodies compared with its effect on the most common version of the virus prevalent in U.S. trials.
Their findings were published in the New England Journal of Medicine (NEJM).
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 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 B1351 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.
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"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."
Prototype vaccine targeting variant in the works
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 U.S. Food and Drug Administration has not yet released a roadmap for how companies should design trials of coronavirus booster shots.
On Wednesday, Moderna also published a correspondence in NEJM with similar data previously disclosed elsewhere that showed a six-fold drop in antibody levels versus the variant identified in South Africa.
Moderna also said the actual efficacy of its vaccine against this variant is yet to be determined. The company has previously said it believes the vaccine will work against the variant.