We all have blind spots, but maybe some are bigger than others

A question for you. It concerns mask wearing to prevent infection with COVID-19. Which do you find the most convincing evidence for wearing an FFP2 mask as opposed to a surgical mask?

1. A study of 500 surgical mask and FFP2 wearing healthcare workers in which about 100 of them became infected with COVID-19. In other words quite a small study of people becoming infected.
2. Studies of masks that show that an FFP2 reduces the dose by around 95% while for masks it is typically in the range 40 to 60%.

There is no real right or wrong answer here. Personally, I would vote for 2. as a study of 500 people, only 100 of whom became infected is pretty small. Whereas I assume that the lower the dose you inhaled, the lower the risk. So I am all for lowering the potential dose, and if you tell me by switching from surgical masks for FFP2-rated masks I can reduce the dose by about a half, I will do that. But I am nobody’s idea of one of “world’s most eminent scientists” and they went hard for option 1., completely passing on 2.

The Royal Society contains “many of the world’s most eminent scientists”, and indeed contains many smart people. And they have just released a report and series of reviews on Non-Pharmaceutical Interventions (NPIs) for reducing the transmission of airborne diseases such as COVID-19. NPIs are things like social distancing, masks, etc.

Your opinion on the Royal Society’s review of masks by Boulos and coworkers will depend on what you think a review should do. If you think a review should focus to exclusion of all else on carefully reviewing randomised controlled trials (RCTs) and their (somewhat harder to interpret and more prone to bias) cousin, observational studies, then this is the review is for you. If you want to know what FFP2 and surgical masks actually are*, how they work and what the difference is, then there is literally nothing in the review for you. Absolutely zilch. As far as the authors are concerned a surgical mask is just something someone may or may not be wearing in an RCT.

Part of me is actually impressed the authors were so careful and rigorous in ignoring so completely the literature on that looks at how masks work, and what the mask standards are. But another part is not happy that they just surveyed half the relevant literature. As the authors note, RCTs and observational studies are hard to do for masks. But then why rely exclusively on RCTs and observational studies?

To me this does not make sense, but I am not sure what to do about this. I am afraid the Royal Society just reflects an approach (laser focused on RCTs) common to many medical doctors and epidemiologists. Pity it did not consult some of the world’s most eminent physicists and engineers, they could have got a more balanced review.

* FFP2 is not a (physical) mask but a mask standard, it is defined by the European standard EN 149. Similarly, the surgical mask standard is EN 14863. Brief summaries of both are in here.