LONDON (AP) — Soaring infections in Britain driven in part by the omicron variant of the coronavirus rattled Europe on Thursday, prompting new restrictions on the Continent and fueling a familiar dread on both sides of the Atlantic about entering a new phase of the pandemic just in time for the holidays.

Much remains unknown about omicron, but officials increasingly warn that it appears more transmissible than the delta variant, which has already put pressure on hospitals worldwide. With so many questions unanswered, uncertainty reigned over how quickly and how severely to crack down on Christmas travel and year-end parties.

After the U.K. recorded its highest number of confirmed new COVID-19 infections since the pandemic began, France announced Thursday that it would tighten entry rules for those coming from Britain. Hours later, the country set another record, with a further 88,376 confirmed COVID-19 cases reported Thursday, almost 10,000 more than the day before.

In England, the chief medical officer urged people to limit who they see in the festive period. Pubs and restaurants said many people were heeding that advice by canceling Christmas parties, though there has been much debate about what’s OK to do. In the U.S., the White House insisted there was no need for a lockdown, despite signs that omicron was gaining ground there.

Globally, more than 75 countries have reported confirmed cases of the new variant.

In Britain, where omicron cases are doubling every two to three days, omicron was expected to soon replace delta as the dominant strain in the country. The government has accelerated its booster program in response. Authorities in the 27-nation European Union say omicron will be the dominant variant in the bloc by mid-January.

Early data suggests that omicron may be milder but better at evading vaccines — making booster shots more crucial. Experts have urged caution in particular about drawing conclusions because hospitalizations lag behind infections and because many variables contribute to how sick people get.

Even if omicron proves milder on the whole than delta, it may disarm some of the lifesaving tools available and put immune-compromised and elderly people at particular risk. And if it’s more transmissible, more infections overall raise the risk that more cases will be serious.

While experts gather the data, some governments rushed to act, while others sought to calm fears that the new variant would land countries back on square one.

Prime Minister Boris Johnson insisted Thursday that the situation in the U.K. is different from last year because of the widespread use of vaccines and the ability to test.

If people want to attend an event “the sensible thing to do is to get a test and to make sure that you’re being cautious,” he said.

“But we’re not saying that we want to cancel stuff. We’re not locking stuff down, and the fastest route back to normality is to get boosted,” he said.