I think this thread is a decent refutation that the CI lower bound was at 0: "First, the 11% reduction comes from a 30% increase in mask-use. The IV estimate (

I think this thread is a decent refutation that the CI lower bound was at 0: "First, the 11% reduction comes from a 30% increase in mask-use. The IV estimate (naively scaling things linearly) would thus be more like a 37% reduction in COVID from going from zero to universal masking." "Second, we find much larger effects among the elderly (a 35% reduction among 60+ without the above scaling). This suggests that the total reduction in morbidity and mortality from universal masking may be considerably larger than even the 37% number, perhaps more than 50%." "Third, it's not quite an apples to apples comparison because we are estimating the community impact of masks, whereas the vaccine studies only isolate the individual protective effect. The efficacy of vaccines at the population level may be larger than trials imply." https://twitter.com/Jabaluck/status/1433129444940599296 https://twitter.com/Jabaluck/status/1433129444940599296