LONDON — One dose of the Pfizer-BioNTech Covid-19 vaccine offers an immune response similar to that generated by an infection and could also offer protection from variants to people who have previously had the virus, a British study said on Friday (March 26) 

Britain in December opted to extend the gap between doses in its vaccine rollout to up to 12 weeks, with officials saying they were confident in their analysis that initial doses of Pfizer and AstraZeneca vaccines generated some protection.