How much difference do masks, ventilation and social distancing actually make?

Vaccines aside, if you were in any doubt as to the efficacy of mask-wearing, social distancing and ventilation during this pandemic, a new study breaks things down for you. The study itself (in Environmental Science & Technology) is a bit dense and hard to digest, but a quick digest on MLive brings out a few salient points.

For example, going to a crowded movie theatre with poor ventilation and mostly unmasked audience gives you a 14% chance of catching the virus, provided no-one speaks before and after (and during). But if people are talking throughout and remain unmasked, that percentage jumps to 54%. If the audience is masked, the chances fall to 5.3% with no talking, and 24% with talking. So, huge differences.

Take gyms as another example. Gyms often complain about how they have been victimized and how working out in a gym is not a risky endeavour, even during the Omicron phase of the pandemic. But heavy exercise in a poorly-vented facility without masks is basically a guarantee for catching the virus, with a 99% probability. Even a short work-out in a well-ventilated gym gives you a 17% chance if unmasked (and would you want to work out with a mask on?). If not well-ventilated and filtered, the chances are around 67% (and how far do you trust what a gym tells you abouts it's ventilation system).

These are just two example from the study, but you get the idea. A similar profile would also apply to restaurants, indoor sports venues, etc. One figure in the original study which tries to compare the relative COVID risks of locations like restaurants, libraries, school classrooms, concert halls, places of worship, supermarkets, etc, is rather hard to interpret and subject to widespread variability. In general terms, though, it places restaurants, concert halls, places of worship and hospital examination rooms relatively high, and libraries, large family dinners and some physical education classes relatively low (with most of the others falling somewhere in between).

I don't know how accurate these figures can be said to be, nor have I looked into the methods used and assumptions made. The bottom line, though, is that ventilation, masks and distance from people speaking or breathing heavily are game-changers. Better yet, don't go into indoor settings any more than necessary.