Britain is in an unparalleled state of crisis. Johnson’s horrifying weekend television address, when he revealed a new, seemingly faster-spreading strain of the coronavirus was tearing through London, has had a domino effect across the world. Over a dozen nations have slammed their doors shut to incoming British travel—most seriously, France has closed its U.K. border for two days, meaning no haulage can make its way in from Europe, raising fears of immediate food shortages days before Christmas…

Many questions about the British variant of the virus remain unanswered. Since the pandemic took hold in March, the world has learned largely what to expect from the coronavirus—but now the rulebook is being frantically rewritten in Britain, where people are facing a mutated virus which appears to be much better at infecting people. There is no evidence to suggest that the mutation makes a COVID infection more deadly, but just increasing transmission would be enough to strain the country’s already-creaking hospitals.

There’s also no evidence to suggest that the approved vaccines won’t work against the mutation, but that doesn’t mean scientists aren’t concerned about that prospect. Ravi Gupta, professor of clinical microbiology at the University of Cambridge, told BBC News: “If we let it add more mutations, then you start worrying… This virus is potentially on a pathway for vaccine escape, it has taken the first couple of steps towards that.” U.S. army scientists are carrying out their own tests to ensure that the vaccine is still effective against the British strain.