Britain’s health secretary has refused to rule out imposing tougher COVID-19 restrictions before Christmas amid the rapid rise of infections and continuing uncertainty about the omicron variant.

Sajid Javid said Sunday that the government was assessing the fast-moving situation and urged the public to be cautious as scientists examine the data. Much is still unknown about the new variant, even as hospitals brace for a surge in infections, he told the BBC.

“There are no guarantees in this pandemic, I don’t think,’’ Javid replied when asked about the potential for new restrictions. “At this point we just have to keep everything under review.”

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Prime Minister Boris Johnson this week reinstated rules requiring face masks in shops and ordered people to show proof of vaccination or a negative coronavirus test before entering night clubs and other crowded venues. But government scientific advisers have recommended more far-reaching restrictions to prevent hospitals from being overwhelmed, according to leaked minutes from a meeting of the Scientific Advisory Group for Emergencies.

Nations across Europe are moving to reimpose tougher measures to stem a new wave of COVID-19 infections spurred by the highly transmissible omicron variant.

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The Dutch government imposed a tough nationwide lockdown starting Sunday in an attempt to rein in sharply rising levels of infections. Alarmed ministers in France, Germany, Austria and Cyprus have tightened travel restrictions.

Ireland imposed an 8 p.m. curfew on pubs and bars and limited attendance at indoor and outdoor events. Paris canceled its New Year’s Eve fireworks.

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London Mayor Sadiq Khan underscored the official concern about the climbing cases and their potential to overwhelm the health-care system by declaring a major incident Saturday, a move that allows local councils in Britain’s capital to coordinate more closely with emergency services.

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The World Health Organization reported Saturday that omicron has been detected in 89 countries. COVID-19 cases involving the variant are doubling every 1.5 to 3 days in places with community transmission and not just infections acquired abroad, the WHO said.