A shortage of vaccines in the European Union—only 4.8% of Europeans have been vaccinated since late December—means the continent hasn’t even started the race against virus mutations that many experts say will define health policy in coming months and years…

The three variants now circulating in Europe are believed to be more easily transmitted, and potentially more dangerous, than the original pathogen that still makes up the majority of cases in Europe. There is also mounting evidence that some strains might be less susceptible to the vaccines currently authorized in the region, according to the European Center for Disease Prevention and Control.

The variant first identified in Britain accounted for 96% of viral samples examined at three major laboratories in England by early February, compared with just over a third at the beginning of December, according to the U.K. government.