The UK’s health minister warned that coronavirus vaccines may be less effective against new variants of the disease, such as those found in South Africa and Brazil, which justifies stricter border controls.“We don’t know the degree of that," Matt Hancock said in an interview on Sky News on Sunday, commenting on the extent of any potential reduced efficacy of the vaccines. “In the meantime, we’ve got to have a precautionary principle that says let’s not bring these new variants back to the UK"Hancock’s warning came as the UK reported it had vaccinated more than 5 million people, including three-quarters of over 80s.