Pfizer and partner company BioNTech announced Tuesday it will launch “a clinical study to evaluate the safety, tolerability and immunogenicity of an Omicron-based” COVID-19 vaccine. The study will test up to 1,420 healthy adults ages 18 to 55, and will be broken down into three parts:

• 615 people who have gotten two doses of the original Pfizer vaccine will get either one or two doses of the Omicron-based vaccine.
• 600 people who have gotten three doses of the original vaccine will get either one more dose of the original vaccine or one dose of the Omicron-based vaccine.
• 205 unvaccinated people will get three doses of the Omicron-based vaccine.

“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,” BioNTech CEO Ugur Sahin said in a news release. Kathryn Jansen, Pfizer’s head of vaccine research and development, added “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 to towards this goal.”

Tuesday’s announcement comes just over a month after research out of South Africa found the country’s Omicron surge decreased the effectiveness of the Pfizer vaccine against infection. The country, which was the first to report the variant, found the Pfizer vaccine was only 33% effective against infection during the surge.

“Emerging data indicate vaccine-induced protection against infection and mild to moderate disease wanes more rapidly than was observed with prior strains,” Sahin said. However, he and Jansen noted vaccines and especially “boosters continue to provide a high level of protection against severe disease and hospitalization with Omicron.”

COVID-19 vaccine makers have been updating their shots to better match omicron in case global health authorities decide the change is needed. It’s not yet clear that a change to the vaccine recipe is needed.