A recent comprehensive examination of international experience  provides a hierarchy of effectiveness of public health interventions. The most effective interventions, as measured by the change in the effective reproduction number (Rt), include the cancellation of small and mass gatherings, closure of educational institutions, border restrictions, lockdowns, restrictions on individual movement, and increased availability and use of PPE such as face masks. Less effective are testing restrictions, public transportation restrictions, airport health checks, and environmental cleaning and disinfection (Figure 1).
Shelter-in-place, lockdown, and curfew orders have a substantial impact on the burden of COVID-19, having reduced Rt from 6.9 to 0.8 over the course of a month in Spain, for example. In an international comparison, stay-at-home orders reduced the percent daily increase in new cases from baseline from 26.9% at baseline to 20.3%, 12.8%, 7.3% at 7, 14, 21 days, respectively.
Closure of schools and workplaces are associated with a modest reduction in the incidence of COVID-19, in the order of 13%.
Travel restrictions lead to a moderate reduction COVID-19 disease burden. A study of 13 European countries found that voluntary reduced mobility occurring prior to government policies decreased the percent change in deaths per day by 9.2%, whereas subsequent government closure policies decreased deaths per day by 14.0%.
An extensive systematic review of SARS, MERS, and SARS-CoV-2 demonstrates that physical distancing of 1 m is associated with a relative risk (RR) of disease transmission = 0.18. The RR decreases two-fold for each additional m increase in distance.
A ban on public gatherings reduces COVID-19 transmission; however, evidence supporting specific gathering size limits is weak. In Germany, gathering restrictions and voluntary behaviour changes had the single greatest effect on the epidemic, reducing Rt by 9.7% per day and the growth rate from 30 to 12% within 2 weeks. Findings from the UK lockdown indicate that the average daily number of contacts decreased from 10.8 before to 2.8 after the lockdown. This was associated with a decrease in Rt from 2.6 to 0.62.
In a systematic review and in modelling studies, mask use by the public is estimated to reduce COVID-19 incidence and deaths by 38% and 47%, respectively.
McCarron, M; Karreman, E; Okpalauwaekwe, U; Henderson, R; Reeder, B; Muhajarine, N; Neudorf, C; Groot, G; Miller, L; Howell-Spooner, B. Which public health interventions are (most) effective in reducing the burden of COVID-19 disease in predominately OECD countries? 2021 Jan 11; Document no.: PH111001 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2020. 54 p. (CEST rapid review report)