A graphic claiming to show the varying transmission risk of Covid-19 between people wearing and not wearing masks has gone viral on Twitter again.
This really isn’t much to ask of us to keep one another safe. pic.twitter.com/v6JlqHyvET
— Giles Paley-Phillips (@eliistender10) November 28, 2021
While the general point that wearing masks offers some protection against infection is true, these numbers aren’t substantiated.
This particular image first went viral in October 2020, and images with the same figures have been critiqued by other fact checkers. In July 2021, Scottish Deputy First Minister John Swinney apologised after sharing the graphic.
There is no evidence that directly backs up the claims made in this graphic.
The closest we’ve found to an explanation is some tweets from a Dublin medical group in May 2020, which evidenced figures in a similar graphic with some research on infection rates among healthcare workers and droplet transmission.
It said that the figures were “of course a gross oversimplification.” Research on healthcare workers is also unlikely to be wholly applicable to the population at large. Data on the effect of masks on reducing the transmission of droplets may not reflect how likely someone is to be infected, because not everyone coming into contact with a droplet carrying the Covid-19 virus is going to become infected by it.
Although there is no evidence to back up the figures used in the post, wider evidence does support the claim that masks reduce the risk of contracting Covid-19, to some extent.
Nature reports that studies show masks can reduce the viral dose someone might receive, and can help protect others by reducing the amount of virus exhaled if the wearer has an infection.
The World Health Organisation advises that, in addition to other actions, “masks are a key measure to suppress transmission and save lives”.