Estimation of the effective reproduction number for SARS-CoV-2 infection during the first epidemic wave in the metropolitan area of Athens, Greece

TL;DR

This study estimates the effective reproduction number of SARS-CoV-2 during Athens' first COVID-19 wave using two widely adopted methods, revealing the impact of lockdown measures and discussing methodological limitations.

Contribution

It compares two prominent methods for estimating R_e and applies them to real data from Athens, Greece, during the initial pandemic wave.

Findings

R_e dropped below 1 around March 15, 2020

Lockdown measures correlated with a decline in R_e

Estimates have high uncertainty during early relaxation phase

Abstract

Herein, we provide estimations for the effective reproduction number $R_e$ for the greater metropolitan area of Athens, Greece during the first wave of the pandemic (February 26-May 15, 2020). For our calculations, we implemented, in a comparative approach, the two most widely used methods for the estimation of $R_e$, that by Wallinga and Teunis and by Cori et al. Data were retrieved from the national database of SARS-CoV-2 infections in Greece. Our analysis revealed that the expected value of Re dropped below 1 around March 15, shortly after the suspension of the operation of educational institutions of all levels nationwide on March 10, and the closing of all retail activities (cafes, bars, museums, shopping centres, sports facilities and restaurants) on March 13. On May 4, the date on which the gradual relaxation of the strict lockdown commenced, the expected value of $R_e$ was slightly below 1, however with relatively high levels of uncertainty due to the limited number of notified cases during this period. Finally, we discuss the limitations and pitfalls of the methods utilized for the estimation of the $R_e$, highlighting that the results of such analyses should be considered only as indicative by policy makers.