Impact of stringent non-pharmaceutical interventions applied during the second and third COVID-19 epidemic waves in Portugal, 9 November 2020 to 10 February 2021: an ecological study.

BackgroundNon-pharmaceutical interventions (NPIs) were implemented worldwide to control the spread of SARS-CoV-2.AimTo evaluate the impact of tiered NPIs and a nationwide lockdown on reduction of COVID-19 incidence during the second and third epidemic waves in Portugal.MethodsSurveillance data on laboratory-confirmed COVID-19 cases were used to conduct an interrupted time series analysis to estimate changes in daily incidence during a second wave tiered NPI period (9 November-18 December 2020), and a third wave lockdown period without (15-21 January 2021) and with school closure (22 January-10 February 2021).ResultsSignificant changes in trends were observed for the overall incidence rate; declining trends were observed for tiered NPIs (-1.9% per day; incidence rate ratio (IRR): 0.981; 95% confidence interval (CI): 0.973-0.989) and a lockdown period without (-3.4% per day; IRR: 0.966; 95% CI: 0.935-0.998) and with school closure (-10.3% per day, IRR: 0.897; 95% CI: 0.846-0.951). Absolute effects associated with tiered NPIs and a lockdown on a subsequent 14-day period yielded 137 cases and 437 cases per 100,000 population potentially averted, respectively.ConclusionOur results indicate that tiered NPIs implemented during the second wave caused a decline in COVID-19 incidence, although modest. Moreover, a third wave lockdown without school closure was effective in reducing COVID-19 incidence, but the addition of school closure provided the strongest effect. These findings emphasise the importance of early and assertive decision-making to control the pandemic.