Abstract

Background
Portugal reported its first cases of covid-19 on 2nd March 2020. In response, a lockdown was declared on 22nd March, following the closure of schools and the initiation of remote working where possible. Without a vaccine, non-pharmacological interventions (NPIs) such as lockdowns have become crucial tools in controlling infectious diseases. Our study aims to provide a quantitative assessment of the impact of lockdown measures on the transmission of covid-19 and their effectiveness in reducing disease spread.
Methods
A Susceptible-Exposed-Infected-Removed (SEIR) model was created to represent the pandemic during the first 70 days of COVID-19 in Portugal, between 22th February and 1st May. Using Bayesian methods, the 95% Credible Interval (95%CrI) was calculated for the effective reproductive number (Rt), final impact of the NPI, and time to reach 50% of its impact. Cases prevented by this NPI in the first 15 days after its introduction were estimated using a counterfactual scenario.
Results
Preliminary results show that Rt on the first day was estimated as 2.62 (95%CrI: 2.11;3.49) and was reduced to a minimum of 0.80 (95%CrI: 0.76; 0.84). Lockdown caused a reduction of 68.6% (95%CrI: 59.2%; 77.5%) to our Rt, achieving 50% of its final effect in 0.07 (95%CrI: 0; 0,39) days. A total of 115968 (95%CrI: 97851; 141571) cases were prevented thanks to the NPI.
Discussion and Conclusions
Lockdown and other NPIs effectively reduced the Rt to below 1, leading to a decline in new cases and control of the outbreak. This may be affected by the population's adherence to the NPI. This approach provides new insights into the impact of NPI and thus aid in decision making for future disease outbreaks. Lockdowns and other NPIs are effective public health measures that should be put in place as soon as possible to prevent excessive mortality and overburdening health services.