Pfizer and BioNTech have commenced a study to determine the safety and immunogenicity of a third dose of their Covid-19 vaccine BNT162b2 against the new SARS-CoV-2 variants.

The third dose of BNT162b2 is planned to be administered as a 30µg booster, in up to 144 US participants in Phase 1/2/3 trial, after 6 to 12 months from receiving their initial two-dose regimen.

Pfizer and BioNTech said that the study will evaluate the safety and tolerability of a third vaccine dose regardless of the level of antibody titers of the trial participant.

Also, the companies intend to study the sera from the study participants to determine its capability to neutralise new strains of SARS-CoV-2.

Pfizer chairman and chief executive officer Albert Bourla said: “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.

“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.”

Pfizer and BioNTech have started discussions with regulatory authorities, including the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA), regarding a separate registration-enabling clinical study.

The study is planned to evaluate a variant-specific vaccine against the B.1.351 lineage viruses, first identified in South Africa.

The variant-specific vaccine is developed from mRNA sequence modification of the two-dose Pfizer-BioNTech Covid-19 vaccine.

Pfizer-BioNTech Covid-19 Vaccine has not been approved by the US FDA, but was granted FDA under an Emergency Use Authorization (EUA) to prevent Covid-19 in people aged 16 years and above.

The companies have recently commenced a Phase 2/3 study to further evaluate their Covid-19 vaccine candidate BNT162b2 in healthy pregnant women.