German biotech company BioNTech and US pharmaceutical Pfizer announced on Monday promising early results from their phase 3 clinical trial for a vaccine against SARS-CoV-2, the virus that causes COVID-19.

These early results are what is known as an ‘interim analysis’. It’s an early look at the data before a study is complete, to understand if there is any indication of whether the vaccine might work.

Currently, this trial has enrolled 43,538 volunteers, giving half the volunteers two doses of the vaccine and the other half two doses of a placebo.

These volunteers then continued their normal lives, but they were monitored for any symptoms that could be COVID-19, with testing to confirm.