Estimating COVID-19 cases and deaths prevented by non-pharmaceutical interventions in 2020-2021, and the impact of individual actions: a retrospective model-based analysis

Fair, K.; Karatayev, V.; Anand, M.; Bauch, C.

Simulation models from the early COVID-19 pandemic highlighted the urgency of applying non-pharmacetical interventions (NPIs), but had limited empirical data to use. Here we use data from 2020-2021 to retrospectively model the impact of NPIs. Our model represents age groups and census division in Ontario, Canada, and is parameterised with epidemiological, testing, demographic, travel, and mobility data. The model captures how individuals adopt NPIs in response to reported cases. The model predicts that school/workplace closure and individual NPI adoption together reduced the number of deaths in the best-case scenario for the case fatality rate (CFR) from 174411 [CI: 168022, 180644] to 3383 [CI: 3295, 3483] in the Spring 2020 wave. In the Fall 2020/Winter 2021 wave, the introduction of NPIs in workplaces/schools reduced the number of deaths from 17291 [CI: 16268, 18379] to 4167 [CI: 4117, 4217]. Deaths were several times higher in the worst-case scenario for the CFR. We also estimated that each additional 7-11 (resp. 285-452) individuals who choose to adhere to NPIs in the first wave prevented one additional infection (resp., death under a best-case scenario). Our results show that the adoption of NPIs prevented a public health catastrophe.