Pfizer-BioNTech Evaluating Third COVID-19 Vaccine Dose for Variants

February 25, 2021
Kevin Kunzmann

The new trial comes at a time when the FDA has provided guidance on navigating immunogenicity trials for vaccines designed against more transmissible SARS-CoV-2 strains.

Pfizer and BioNTech has launched a safety and immunogenicity assessment for a third dose of its coronavirus 2019 (COVID-19) vaccine BNT162b2 to consider a booster intended to provide immunity to circulating potentially new SARS-CoV-2 variants.

The study, which will recruit participants from the companies’ phase 1 trial in the US, will observe a 30 mcg booster of the current vaccine 6-12 moths after the two-dose mRNA vaccine regimen had been administered.

Investigators hope to observe an early assessment of safety and immunogenicity with the third dose in up to 144 participants across 2 cohorts: 18-55 and 65-85 years old.

Participants will be studied at baseline, then 1 week and 1 month after administration, for the ability of their sera to neutralize particular SARS-CoV-2 strains.

As planned in the vaccine developers’ trial program, all participants would be assessed for the coming 2 years.

While the trial is initiated, Pfizer and BioNTech are continuing discussion with regulatory authorities including the US Food and Drug Administration (FDA) on the matters of a registration-enabling clinical trial evaluating a variant-specific vaccine with a modified RNA sequence.

The vaccine would feature a new construct based on the B.1.351 lineage, better known as the highly transmissible South Africa variant.

Earlier this week, the FDA provided updates to October 2020 COVID-19 guidelines for vendors submitted for Emergency Use Authorization (EUA), advising that vaccines modified to respond to prominent virus variants be assessed through immunogenicity trials comparing immune responses of the modified vaccine against the targeted SARS-CoV-2 variant, with that of the prototype vaccine against its targeted virus.

Per the new advisory, immunogenicity trials may be conducted in a single age group, with results extrapolated to other groups for which the prototype vaccine had already been authorized, as well as previously infected individuals in the same age groups.

Modified vaccines may be assessed for safety outcomes as simple as solicited local and systemic adverse events observed daily for ≥7 days after each study vaccination, as well as serious and other unsolicited adverse events during the immunogenicity study.

With consideration to this new guidance, Pfizer and BioNTech are pursuing regulation of future modified mRNA vaccines through a pathway akin to those in place for annual flu vaccines.

Just yesterday, new data published in The New England Journal of Medicine showed two-dose BNT162b2 has reduced real-world population risk of symptomatic COVID-19 by 94% in Israel ≥7 days following the booster shot. Investigators acknowledged the significant presence of the B.1.1.7 lineage—better known as the England variant—in the Israel population at the time of their assessment, but a rarity of B.1351 cases.

“While we have not seen any evidence that the circulating variants result in a loss of protection provided by our vaccine, we are taking multiple steps to act decisively and be ready in case a strain becomes resistant to the protection afforded by the vaccine,” Albert Bourla, Chairman and Chief Executive Officer of Pfizer, said in a statement. “This booster study is critical to understanding the safety of a third dose and immunity against circulating strains.