A post on Instagram claims a Stanford study has shown face masks are ineffective at blocking Covid-19 viral particles.
We have written about the study cited before. The author was not affiliated with Stanford University and the paper was strewn with basic errors, misrepresenting legitimate research on the effect of face masks.
The study has since been retracted.
The post goes on to claim that face masks have gaps measuring 55,000 nanometres across while the Covid-19 virus is just 140 nanometres, suggesting face masks are useless.
The gaps in face masks can be much larger than the size of a viral particle. That doesn’t mean face masks are useless.
For one thing, Covid-19 is often spread by viral particles carried in saliva droplets that are exhaled. These droplets are much larger than a viral particle itself, and so are more likely to be blocked by a face mask.
Also, as explained in The Conversation by epidemiologists from McMaster University, Leiden University and the Karolinska Institutet in Stockholm, “at this microscopic level, the thread has thickness, or depth, so the gap is more a tunnel than a window. Microfilaments from broken or irregular threads project into the gap.”
In other words, even if there are relatively large gaps in mask fabric, that’s not to say a particle is guaranteed to move unimpeded through that gap. It would need to be travelling at an angle so as to not impact with the material, and avoid any stray threads which go some way to filling in the gaps in the fabric weave.
There is also evidence that masks do stop the transmission of viral particles.
A study published last year tested the efficacy of face masks, by measuring the presence of viral particles in exhalations of people wearing surgical face masks compared to those who weren’t.
It found “surgical face masks significantly reduced detection of influenza virus RNA in respiratory droplets and coronavirus RNA in aerosols, with a trend toward reduced detection of coronavirus RNA in respiratory droplets.”
A recent trial in Bangladesh found that people issued with surgical masks were 11% less likely to be infected with Covid-19. The results suggested cloth masks also reduce risk but the results were not statistically significant.
The World Health Organisation describes face masks as “a key measure to suppress transmission and save lives”.