Austria imposed a lockdown on people unvaccinated against the coronavirus on Monday as winter approaches and infections rise across Europe, with Germany considering tighter curbs and Britain expanding its booster programme to younger adults.

Europe has again become the epicentre of the pandemic, prompting some countries to consider reintroducing restrictions in the run-up to Christmas and stirring debate over whether vaccines alone are enough to tame Covid-19.

The disease spreads more easily in...