Advertisement
Not quite, says Professor Hoffmann. âThatâs what itâs often interpreted as. It actually means there was a 95 per cent reduction in new cases of COVID-19 in the vaccine group, compared to the placebo group.â
Thatâs a complex idea, so letâs break it down. In Pfizerâs phase 3 trial, 18,198 people got the vaccine and 18,325 got a placebo. There were eight cases of COVID-19 in the vaccinated group and 162 in the placebo group. Scientists can then calculate the infection risk for people given a placebo: 0.88 per cent. For people given the vaccine: 0.04 per cent. That allows scientists to calculate the difference between the groups in the risk of being infected with COVID-19: about 0.8 per cent. In this trial, the vaccine had a