Are the trial participants exposed to the virus purposefully or is the result that none of participants developed covid just from regular daily living?
There's a (blinded) control group so purely based on how deeply unethical it would be to purposefully expose them to the virus I'd wager they were 'natural' occurrences.
I understand how it could be unethical, though I'd be more confident in a study that had purposeful exposure - how can we say the vaccine really was the means of protection, and not just the current measures?
The study compares how many people in the experimental group and control group develop symptomatic COVID-19. In this case 11 people in the experimental group developed COVID-19 versus 185 in the control group. Thus the vaccine is approximately 185 / (185 + 11) = 94% effective, assuming both groups behaved similarly.
If the control group intentionally avoided exposure more than the experimental group, then the vaccine is even more effective than the study result. This is a blinded study though, so participants don't know which group they're in unless they go out of their way to find out (eg. taking an antibody test).
