Transmission dynamics and control of COVID-19 in Chile, March-June, 2020
Authors: Tariq Amna , Undurraga Eduardo A. , Laborde Carla Castillo , Vogt-Geisse Katia , Luo Ruiyan , Rothenberg Richard , Chowell Gerardo 
Published: May 2020

Since the detection of first case of COVID-19 in Chile on March 3rd, 2020, a total of 301019 cases including 6434 deaths have been reported in Chile as of July 7th, 2020. In this manuscript we estimate the reproduction number during the early transmission phase in Chile and study the effectiveness of control interventions by conducting short-term forecasts based on the early transmission dynamics of COVID-19. We also estimate the reproduction number and conduct short term forecasts for the most recent developments in the epidemic trajectory of COVID-19 in Chile (May 9th-July 7th, 2020) to study the effectiveness of re-imposition of lockdowns in the country. The incidence curve in Chile displays early sub-exponential growth dynamics with the scaling of growth parameter,p, estimated at 0.8 (95% CI: 0.7, 0.8) and the reproduction number, estimated at 1.8 (95% CI: 1.6, 1.9). Our analysis emphasizes that the control measures at the start of the epidemic significantly slowed down the spread of the virus. However, easing of the COVID-19 restrictions and spread of virus to the low income neighborhoods in May led to a new wave of infections, followed by the re-imposition of lockdowns in Santiago and other municipalities. These measures have decelerated the virus spread withRestimated at ~0.87(95% CI: 0.84, 0.89) as of July 7th, 2020. Our current findings point that the sustained transmission of SARS-CoV-2 in Chile is being brought under control. The COVID-19 epidemic followed an early sub-exponential growth trend (p~0.8) that transformed into a linear growth trend (p~0.5) as of July 7th, 2020. While the broad scale social distancing interventions have slowed the virus spread, the number of new COVID-19 cases continue to accrue, underscoring the need for persistent social distancing and active case detection and isolation efforts to bring epidemic under control.

Author summary

In context of the ongoing COVID-19 pandemic, Chile is one of the hardest hit countries in Latin America, struggling to contain the spread of the virus. In this manuscript we employ renewal equation to estimate the reproduction number for the early ascending phase of the COVID-19 epidemic and the most recent time period to guide the magnitude and intensity of the interventions required to combat the COVID-19 epidemic. We also generate short terms forecasts based on the epidemic trajectory using phenomenological models and assess counterfactual scenarios to understand any additional resources required to contain the spread of virus. Our results indicate early sustained transmission of SARS-CoV-2. However, the initial control measures at the start of the epidemic significantly slowed down the spread of the virus whose effect is visible two weeks after the implementation of interventions. Easing of the COVID-19 restrictions in May led to a new wave of infections, followed by the re-imposition of lockdowns in Santiago and other municipalities. While the broad scale social distancing interventions have slowed the most recent spread of the virus spread, the number of new COVID-19 cases continue to accrue, underscoring the need for persistent social distancing efforts to bring epidemic under control.