How close is a vaccine?

Later today, we're expecting to see the early-stage trial data on one of the most advanced coronavirus vaccines in development, from AstraZeneca and Oxford University.

The UK has already invested in 100m doses in the hope that it might stop the Covid-19 pandemic, as well as signing deals for 90m doses of other promising vaccines.

But why is a vaccine so important and how close are we to getting one? You can find out in this guide to the vaccine race.