Pfizer and BioNTech on Tuesday announced the initiation of a clinical study to evaluate the safety, tolerability and immunogenicity of an Omicron-based vaccine candidate. The study will evaluate up to 1,420 healthy adults aged between 18 and 55. The study will have three cohorts examining different regimens of the current Pfizer-BioNTech COVID-19 vaccine or an Omicron-based vaccine.