Two years of SARS-CoV-2 pandemic and COVID-19 in Lombardy, Italy.

Lombardy, the largest and most densely populated Italian region, was severely hit in February 2020 by the first pandemic wave of SARS-CoV-2 and associated COVID-19. Since then, additional infection waves spread in the region. The aim of this study was to compare the first with the subsequent waves using the administrative database of the Lombardy Welfare directorate. In the time frames of the four 2020-2022 waves, the absolute number of infected cases, sites of management and crude mortality rate associated with SARS-CoV-2 positivity were extracted from the database. Infected cases progressively increased in the region by approximately 5-fold in the second versus the first wave, 4-fold in the third and 20-fold during the most recent wave mainly associated with the omicron variant. The crude death decreased from 18.7% in the first to 2% in the second and third wave to reach a 0.3% nadir at the time of the fourth wave. This study confirms that in Lombardy outcomes of public health and health-care relevance such as deaths and number of hospitalizations declined dramatically across the four virus waves and reached very low values in 2022 when, at variance with the first three SARS-CoV-2 waves, the majority of infected cases had been previously vaccinated.