How about that? Though the protection offered is far from 100%, surgical masks do reduce the spread of Covid-19. That's according to a large-scale study led by researchers at Stanford Medicine and Yale University.
This study enrolled 350,000 people in 600 Bangladesh villages. People in control villages were offered free masks, were encouraged to use them properly (covering nose and mouth), were reminded (not forced) to wear them when seen unmasked and community leaders also wore surgical masks. The result was an 11% drop in the overall infection rate and a 35% decrease in people over 60.
Interestingly, in these control villages, less than 50% of the population wore masks despite the encouragement. In the control villages, there was also a slight increase in social distancing. The study also found that surgical masks are more effective than cloth masks.
You can find the data from this study here.