German biotechnology company BioNTech and U.S. company Pfizer have started clinical trials of an Omicron-based COVID-19 vaccine candidate in healthy adults 18 through 55 years of age, the companies said on Tuesday.

The trials would evaluate the safety, tolerability and immunogenicity of the vaccine candidate, according to a joint statement. The study would involve up to 1,420 participants.

"This study is part of our science-based approach to develop a variant-based vaccine that achieves a similar level of protection against Omicron as it did with earlier variants but with longer duration of protection," said Ugur Sahin, chief executive officer (CEO) and co-founder of BioNTech.

The first group of participants, around 600 volunteers, have already received two doses of the BioNTech/Pfizer COVID-19 vaccine between 90 days and 180 days before the start of the study. They would receive one or two doses of the new Omicron-based vaccine, according to the statement.

The second group, almost as large, would include individuals who have already received three vaccine doses and who would then receive one dose of the BioNTech/Pfizer COVID-19 vaccine or the Omicron-based vaccine.

The third group would include around 200 unvaccinated people, who have not previously had COVID-19. People in this group would receive three doses of the new Omicron-based vaccine, according to the statement.

"Staying vigilant against the virus requires us to identify new approaches for people to maintain a high level of protection, and we believe developing and investigating variant-based vaccines, like this one, are essential in our efforts towards this goal," said Kathrin Jansen, Pfizer's senior vice president.