Could a third vaccine shot better protect against SARS-CoV-2 variants?

Pfizer/BioNTech and Moderna are testing whether a third dose of their COVID-19 vaccines could better protect against new virus variants.

Pfizer (NYSE:PFE) and BioNTech (NSDQ:BNTX) announced today that participants from their Phase 1 study will be offered the opportunity to receive a 30-µg booster of the current vaccine 6 to 12 months after receiving their initial two doses. The two companies are also in discussions with regulatory authorities including the U.S. FDA and European Medicines Agency about a registration-enabled clinical study of a vaccine with a modified mRNA sequence geared toward the South African variant.

“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. This booster study is critical to understanding the safety of a third dose and immunity against circulating strains,” Pfizer CEO Albert Bourla said in a news release.

“At the same time, we are making the right investments and engaging in the appropriate conversations with regulators to help position us to potentially develop and seek authorization for an updated mRNA vaccine or booster if needed,” Bourla said.

Moderna (NSDQ:MRNA) meanwhile announced yesterday that it had started shipping doses to NIH of a version of its vaccine that is geared toward the South African variant — a move that allows a Phase 1 clinical trial to start. Moderna has also started dosing a clinical trial cohort with a third 50-µg dose of its already authorized vaccine.

“As we seek to defeat COVID-19, we must be vigilant and proactive as new variants of SARS-CoV-2 emerge. Leveraging the flexibility of our mRNA platform, we are moving quickly to test updates to the vaccines that address emerging variants of the virus in the clinic,” said Moderna CEO Stéphane Bancel.

If boosters prove to be effective against emerging variants, regulatory authorization would likely be rapid. But the use of boosters to fight variants could also complicate vaccine logistics and require compliance from the public to work.