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Efficacy of Localized Lockdowns in the SARS-CoV-2 Pandemic

Our take —

This study, available as a preprint and thus not yet peer-reviewed, demonstrated that the effectiveness of local lockdowns on COVID-19 transmission are dependent on the duration of intervention and the spillover effects from neighboring municipalities using municipalities in Chile as a case study. Due to spillover events, local control by itself may not be sufficient to control epidemic growth. Greatest reductions in transmission and case numbers could be achieved by extending the lockdown period of the target and neighboring municipalities.

Study design

Modeling/Simulation

Study population and setting

Authors used the daily time series of COVID-19 cases reported by the Ministry of Health of Chile between March 1 and mid-July, 2020 and adjusted this by the delay from symptom onset to report to reconstruct the epidemic curve by date of onset. Census data and household survey data were also incorporated. Transmission in each municipality was characterized by the instantaneous reproduction number allowing for interactions between neighboring municipalities as different municipalities were subject to different localized lockdown policies. Demographic and economic factors that differed by municipality and could affect transmission such as age, sex, sanitation infrastructure, overcrowding, and monthly income were accounted for. The authors used a causal inference framework to explore the impact of counterfactual lockdown policies of different durations.

Summary of Main Findings

Authors found that the effectiveness of local lockdowns are highly affected by the duration of the local lockdown and the level of spillover from neighboring municipalities that may have different levels of transmission and under different control measures. In three municipalities of Greater Santiago a local lockdown lasting 3-weeks longer would have decreased the reproduction number further, preventing 143 per 100,000; 59 per 100,000; and 267 per 100,000 population in Lo Barnechea, Providencia, and Santiago respectively, representing a 33-62% reduction in reported cases in that time period. Authors estimate that these reductions would have been even greater had the neighboring municipalities also extended their local lockdowns.

Study Strengths

Authors used an integrated dataset of daily reported COVID-19 cases adjusted for reporting delays, household survey, and census data to reconstruct the epidemic course in Chile. The natural variation in local lockdowns implemented in each municipality with varying durations were used to explore their effectiveness in reducing transmission. Authors also accounted for the interconnected nature of neighboring municipalities and explored varying counterfactuals and their effect on the epidemic.

Limitations

As data by date of symptom onset were not available, authors had to reconstruct the epidemic curve accounting for the onset to reporting delay to estimate the reproduction number over time. Information on testing efforts are not provided so it is difficult to determine whether the increase in case numbers, particularly early in the epidemic are a true increase in transmission, or an increase in case finding.

Value added

This study provides insights into the effectiveness of local lockdowns and the importance of considering the spatial interconnectedness of neighbouring municipalities and their local interventions.

This review was posted on: 16 November 2020