On Jan. 25, 2022, Pfizer and BioNTech announced the initiation of a clinical study to evaluate the safety, tolerability and immunogenicity of an Omicron-based vaccine candidate in healthy adults 18 through 55 years of age.

The study planned three cohorts that examined different regimens of the current Pfizer-BioNTech COVID-19 vaccine or an Omicron-based vaccine.