Covid-19: Pfizer/BioNTech vaccine Q&A
The UK is the first country in the world to approve the Pfizer/BioNTech coronavirus vaccine.
Britain's medicines regulator, the MHRA, has said the vaccine, which offers up to 95% protection against Covid-19, is safe to be rolled out.
It paves the way for mass vaccination, but how was it approved so quickly and who should get it first?
BBC World News speaks to the London School of Hygiene and Tropical Medicine’s Prof Brendan Wren to find out more.