“Our message is: Don’t freak out, the plan remains the same: Speed up the administration of a third booster shot,” Ugur Sahin, who co-founded BioNTech and invented one of the first COVID-19 vaccines, told The Wall Street Journal.

“Our belief [that the vaccines work against Omicron] is rooted in science: If a virus achieves immune escape, it achieves it against antibodies, but there is the second level of immune response that protects from severe disease—the T-cells,” he said.

“Even as an escape variant, the virus will hardly be able to completely evade the T-cells," he said.

Meanwhile, the head of the UN health agency has criticized “blunt” and “blanket” measures taken by countries in the past few days to stop the spread of the Omicron variant.

In a statement on Tuesday, the World Health Organization Director-General said that it was “deeply concerning” that Botswana and South Africa, where the new variant was first identified, were “being penalized by others for doing the right thing”.

Dozens of countries have imposed travel bans on the southern African nations since the mutation was discovered at the end of last week.

Tedros said that while it was understandable that all countries should want to protect their citizens, Omicron was still a largely unknown threat.

And he insisted that the world should not forget “that we are already dealing with a highly transmissible, dangerous variant – the Delta variant, which accounts for almost all cases globally”.

As scientists race to understand how virulent and transmissible the new Omicron variant is, WHO is urging the use of all available precautions to stop the spread.

“As we don't have any full picture of this variant, as long as we don't know how well the existing vaccines are working…we need to use the measures that we know work,” said Christian Lindmeier, WHO spokesperson, during a scheduled briefing in Geneva on Tuesday.

These measures include “mask-wearing…ventilating a room if possible, as often as possible, keeping the normal hand and body hygiene...We know these measures work”.

The WHO’s message comes as reports indicated potential concern voiced by the chief of vaccine manufacturer, Moderna, that existing shots may not be as effective against the new variant as previous ones, such as Delta.