Italy is one of the countries that has been most affected by the coronavirus disease (COVID-19) pandemic, and Lombardy is the region of Italy with the highest number of infected patients . On October 30, 2020, the overall number of confirmed COVID-19 cases in Lombardy was 186825, corresponding to about 30% of all cases in Italy .
During the COVID-19 first wave, the peak incidence in Italy was reached on March 21, 2020 . After a progressive and significant descent, since late August 2020, the infections have started to rise again.
On March 21, 2020, the number of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in Italy was 6557. On October 30, 2020, the number of new SARS-CoV-2 infections was 31084 . However, on March 21, the number of newly hospitalized patients with SARS-CoV-2 infection was 1890, with a hospitalization rate (HR) of 28.8% (10.7% in intensive care units), whereas the number of new hospitalized patients with SARS-CoV-2 infection on October 30 was 1125 with a HR of 3.6% (8.4% in intensive care units) . In addition, while on March 21, the number of new deaths was 793 with a daily case fatality rate (dCFR, calculated as the reported number of new COVID-19 deaths divided by the total number of positive cases) of 1.8 %, the number of new deaths on October 30 was 199 with a dCFR of 0.06% .
Similarly, on March 21, the daily HR and dCFR in Lombardy were 17.4% and 3%, respectively, whereas the daily HR and dCFR on October 30 were 4.1% and 0.06%, respectively .
The thing worth highlighting is that Lombardy had a significantly higher dCFR than the rest of Italy only in the first COVID-19 wave.
According to these preliminary data, it would appear that in Italy, especially in Lombardy, the COVID-19 second wave is less severe (reduced daily HR) and deadly (reduced dCFR) than the first one was. In particular, it should be stressed that in Lombardy the dCFR in the COVID-19 second wave (calculated on October 30) was about 50 times lower than in the first one (calculated on March 21).
However, this difference could be affected by several factors, including the different number of swabs performed in the two waves. In fact, while on March 21, the number of nasal/pharyngeal swabs was 26336 (with a 24.9% positivity rate), the number of nasal/pharyngeal swabs on October 30 was 215085 (with a 14.5% positivity rate) . Therefore, it is not yet clear whether the COVID-19 second wave in Italy, specifically in Lombardy, is less severe and deadly than the first one.
Considering the close relationship between pulmonary involvement, in-hospital mortality [2, 3], and the need for ventilatory support [3, 4], the main purpose of this study was to quantify the radiographic severity of COVID-19 pneumonia during the second wave and compare it with that of the first one. In addition, to further test whether the severity of the second wave is indeed lower than that of the first wave, we also compared the use of mechanical ventilation (MV) in the two waves.