Pfizer Inc. (NYSE: PFE) and BioNTech SE (Nasdaq: BNTX) 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 will have three cohorts examining different regimens of the current Pfizer-BioNTech COVID-19 vaccine or an Omicron-based vaccine.