Pfizer developing booster shot to combat COVID-19 Delta variant

In an email to Global News, the companies confirmed that they have seen "encouraging data in the ongoing booster trial" of the vaccine that suggests a third shot of the two-dose Pfizer-BioNTech vaccine has the capacity to offer the “highest levels” of protection against known COVID-19 variants, including Delta.

The data was based on trials where the booster was administered six months after a second dose, Pfizer said. The companies said they believe that "a third dose may be beneficial within six to 12 months following the second dose" for best results.

Pfizer said it expects to submit data to U.S. and European regulators "in the coming weeks" to get approval for the booster, and will have more definitive data to share "soon."

The updated version of the Pfizer COVID-19 vaccine targets "the full spike protein of the Delta variant," according to the companies' emailed statement and the drugmakers expect that a third dose will boost "antibody titers even higher, similar to how the third dose performs for the Beta variant (B.1.351)."

Pfizer Chief Scientific Officer Mikael Dolsten said Thursday that the vaccine is "highly active against the Delta variant."

But after six months, "there likely is the risk of reinfection as antibodies, as predicted, wane," he added.

Pfizer's own data from the United States showed an erosion of the vaccine efficacy to the mid-80s after six months, Dolsten said, against the variants that were circulating there in the spring.

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However, he said that data from Israel and Britain suggests that even with waning antibody levels, the vaccine remains around 95 per cent effective against severe disease.

An additional email sent by Pfizer Thursday confirmed that work is underway to keep improving the vaccine so that it more fully targets the Delta variant. Clinical trials for the update vaccine are set to begin in August, subject to regulatory approvals.

The vaccine, developed with German partner BioNTech SE , showed 95 per cent efficacy in preventing symptomatic COVID-19 in a clinical trial the companies ran last year.

Dolsten said that early data from the company's own studies shows that a third booster dose generates antibody levels that are five to 10-fold higher than after the second dose, suggesting that a third dose will offer promising protection.

He said multiple countries in Europe and elsewhere have already approached Pfizer to discuss booster doses, and that some may begin administering them before a potential U.S. authorization.

Dolsten further said that he believes booster shots are particularly important in older age groups.

The companies are conducting pre-clinical and clinical tests to confirm this hypothesis and the "first batch of the mRNA for the trial has already been manufactured at BioNTech’s facility in Mainz, Germany," the statement from Pfizer and BioNTech said.

Dr. Eric Topol, a professor of molecular medicine and director of the Scripps Research Translational Institute in La Jolla, California, said basing the decision on waning antibody protection ignores the role of important other parts of the immune response, including memory B cells, which can make antibodies on demand when challenged by the virus.

"You need better studies to be able to assert that. It isn't just neutralizing antibodies," Topol said.

However, according to Dr. William Schaffner, a vaccine expert at Vanderbilt University medical Center, even if Pfizer succeeds in getting its booster approved for use by the FDA, that is only the first step. The booster would still need to be reviewed and recommended by advisers to the U.S. Centers for Disease Control and Prevention.

"It's not automatic by any means," he said. Schaffner said realistically, most of the public health bandwidth in the United States is still focused on encouraging Americans to get their first and second doses of the vaccine.