Geographic negative correlation of estimated incidence between first and second waves of coronavirus disease 2019 (COVID-19) in Italy

Abstract

In this short communication, we investigate whether the intensity of the second wave of infection from SARS-CoV-2 that hit Italy in October–November–December 2020 is related to the intensity of the first wave, which took place in March–April 2020. We exploit the variation of the wave intensities across the 107 Italian provinces. Since the first wave has affected not only different regions, but also different provinces of the same region, at a heterogenous degree, this comparison allows useful insights to be drawn about the characteristics of the virus. We estimate a strong negative correlation between the new daily infections among provinces during the first and second waves and show that this result is robust to different specifications. This empirical result can be of inspiration to biologists on the nature of collective immunity underlying COVID-19.