The highly transmissible strain has eluded some of the protection provided by the original two-dose vaccine regimen.
Announcing the move on Tuesday, the companies said they plan to test the immune response generated by the Omicron-based vaccine both as a three-shot regimen in unvaccinated people and as a booster shot for people who already received two doses of their original vaccine.
They are also testing a fourth dose of the current vaccine against a fourth dose of the Omicron-based vaccine in people who received a third dose of the Pfizer/BioNTech vaccine three to six months earlier.
The companies plan to study the safety and tolerability of the shots in the more than 1,400 people who will be enrolled in the US trial.
“While current research and real-world data show that boosters continue to provide a high level of protection against severe disease and hospitalization with Omicron, we recognise the need to be prepared in the event this protection wanes over time and to potentially help address Omicron and new variants in the future,” Pfizer’s head of vaccine research and development, Kathrin Jansen, said in a statement.
Depending on the amount of clinical trial data required by regulators, it may not be possible to realise a current plan to launch an Omicron-targeting vaccine by the end of March, BioNTech said.
Pfizer has said that two doses of the original vaccine may not be sufficient to protect against infection from the Omicron variant, and that protection against hospitalisations and deaths may be waning.
However the US Centers for Disease Control and Prevention says a third dose of an mRNA vaccine like the Pfizer/BioNTech vaccine has provided 90 per cent protection against hospitalisation due to COVID-19.
Some countries have already started offering additional booster doses, but a recent study from Israel showed that while a fourth dose of an mRNA vaccine boosted antibodies, the level was not high enough to prevent infection by the Omicron variant.
The Omicron variant has replaced the Delta variant as the dominant lineage in many parts of the world and Omicron itself is now splitting into different subforms, one of which, BA.2, is causing particular concern.