(Bloomberg) -- The U.K. should remain cautious until officials know the effects of the new omicron variant because it is so easy to pass on, the scientist behind the U.K.’s joint Oxford/AstraZeneca Covid-19 vaccine will warn. 

“The spike protein of this variant contains mutations already known to increase transmisability of the virus but there are additional changes that may mean antibodies induced by the vaccines, or by infection with other variants, may be less effective at preventing infection with Omicron,” Sarah Gilbert, professor of vaccinology at Oxford University, will warn in a BBC TV lecture Monday. 

“Until we know more, we should be cautious, and take steps to slow down the spread of this new variant,” she will say, according to the BBC. “But as we have seen before, reduced protection against infection and mild disease does not necessarily mean reduced protection against severe disease and death.”

The warning came as Prime Minister Boris Johnson’s government said that while people should employ common sense in the run-up to seasonal celebrations, parties should not be canceled altogether. However, Deputy Prime Minister Dominic Raab said he had scaled back his own office party. 

“The government wants people to be able to enjoy Christmas this year,” Raab told Sky News on Sunday. “People should feel free to go and enjoy those celebrations and every employer will think about the right way to do it and I’m the same as everybody else.”

On Saturday, officials announced all travelers arriving in England will be required to take a Covid-19 pre-departure test from Tuesday in an effort to curb the spread of omicron, which has infected about 250 people in the U.K. since it was first detected in the country on Nov. 27. The government also banned travel from Southern Africa and increased the number of countries on its red list that require a 10-day quarantine.

Professor Mark Woolhouse, who is a member of the Scientific Pandemic Influenza Group on Modeling which advises the U.K. government, told the BBC on Sunday that the measures would not make a “material difference” because the variant is already “spreading pretty rapidly.”

“If omicron is here in the U.K., and it certainly is, if there’s community transmission in the U.K., and it certainly looks that way, then it’s that community transmission that will drive a next wave,” he told the Andrew Marr program.

Gilbert will also call for governments to continue funding pandemic preparedness, saying there will be viruses in the future that could pose an even bigger threat than Covid. 

“This will not be the last time a virus threatens our lives and our livelihoods,” she will say. “The truth is, the next one could be worse. It could be more contagious, or more lethal, or both.”

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