The global spread of the omicron variant could have a major impact on the course of the COVID-19 pandemic and the time to contain it is now, before more patients infected by the variant are hospitalized, the World Health Organization (WHO) said on Wednesday.

Governments need to reassess national responses to COVID-19 and speed up vaccination programs to tackle the new variant variant, though it is it too early to say how well existing shots will protect against the new variant, WHO director-general Tedros Adhanom Ghebreyesus said.

"We call on all countries to increase surveillance, testing and sequencing," he told a media briefing. "Any complacency now will cost lives."

The WHO noted early evidence from BioNTech and Pfizer of the effectiveness of their vaccine against omicron.

The German and U.S. companies said on Wednesday a three-shot course of their COVID-19 vaccine was able to neutralize the new omicron variant in a laboratory test, while two doses resulted in lower neutralizing antibodies by a factor of 25.

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Warning against jumping to conclusions from the test, the WHO's chief scientist said it was too soon to say whether the reduction in neutralizing antibodies meant the shot was less effective.

"We do not know that," Soumya Swaminathan told the briefing, adding that coordinated global research efforts were needed.

The WHO also said it would publish a review of its stance on booster doses within days, but with vaccination rates worryingly low in much of the developing world, administering primary doses – rather than boosters – remained its priority.

"Wholesale boosters are not the solution," Swaminathan said.