"We may not have to change the vaccine," he said. "We may be able to get by with the current vaccine, at least for repression of severe disease."

OMICRON-SPECIFIC VACCINE

The World Health Organization classified Omicron on Nov. 26 as a "variant of concern" but said there was no evidence to support the need for new vaccines specifically designed to tackle the variant and its mutations.

Nevertheless, the companies said they would continue efforts to bring an Omicron-specific COVID-19 vaccine to market. Work started on Nov. 25.

They said their planned production of 4 billion doses of the Comirnaty vaccine in 2022 was not expected to change if an adapted vaccine was required. BioNTech said that even if an adapted vaccine was available in March, it would not be broadly available for some time, noting that perhaps 25 to 75 million doses of the new vaccine would be ready at first.

Pfizer scientist Kena Swanson said the company is considering also testing two doses of an Omicron-specific vaccine in currently unvaccinated people.

Pfizer and BioNTech's findings are broadly in line with a preliminary study published by researchers at the Africa Health Research Institute in South Africa on Tuesday, which said Omicron could partially evade protection from two doses of the Pfizer/BioNTech vaccine and suggested a third shot might help fend off infection.

Research on the new variant is still at an early stage. Laboratory analysis at University Hospital Frankfurt in Germany found the ability to mount an antibody response to Omicron in people who had three shots was up to 37 times lower than the response to Delta.

Even so, two shots of the vaccine may still protect against severe disease, Pfizer and BioNTech said.

The vast majority of surface structures on the Omicron spike protein targeted by the T-cells, which typically emerge after vaccination, are not affected by Omicron's mutations, they said.

T-cells are the second pillar of an immune response, alongside antibodies, and are believed to prevent severe disease by attacking infected human cells.

For their analysis, the two companies used a virus that was bio-engineered to have the hallmark mutations of Omicron, known as a pseudovirus, and blood was collected from subjects three weeks after a second vaccine dose or one month after a third.

There is no significant data yet on how vaccines from Moderna, Johnson & Johnson and other drugmakers hold up against the new variant but they are expected to release their own data within weeks.

(Reporting by Ludwig Burger; Editing by Alex Richardson, Edmund Blair, Elaine Hardcastle and Sonya Hepinstall)