A few months back I wrote an article about the state of the evidence on face masks. At that point, there were no good studies looking at the effectiveness of face masks in preventing the spread of covid-19 specifically, but there was a systematic review that looked at all randomized trials that had been done on face masks for the prevention of respiratory infections more generally. That review found that surgical face masks reduced the probability of getting a respiratory infection by around 4% in absolute terms (17% in relative terms).
A very interesting article was recently published in Lancet that sought to understand which factors correlate, on a country level, with covid related outcomes. The study was observational, so it can only show correlation, not causation, but it can still give pretty strong hints as to which factors protect people from covid, and which factors increase the risk of being harmed.
One of the most frequent questions I’ve been getting recently is how accurate I think the covid tests are, and in particular the PCR tests. As it happens, a systematic review has recently been published in Evidence Based Medicine that looks at the covid tests (both PCR and antibody), so I thought it would be interesting to look in to the evidence together. This article gets a bit technical and math-heavy in places, so please bear with me. I think the payoff is worth it.
There has been a lot of controversy over whether face masks decrease the spread of respiratory infections during the covid-19 pandemic. And what is the most sensible thing to do when a topic is controversial? Look at what the evidence says!