Before revision: Among the many aspects that characterize the COVID-19 pandemic, two seem particularly challenging to understand: i), the great geographical differences in the degree of virus contagiousness and lethality which were found in the different phases of the epidemic progression, and , ii) , the potential role of the infected people's blood type in both the virus infectivity and the progression of the disease.
After revision: Among the many aspects that characterize the COVID-19 pandemic, two seem particularly challenging to understand: (i) the great geographical differences in the degree of virus contagiousness and lethality which were found in the different phases of the epidemic progression, and , ii) , the potential role of the infected people's blood type in both the virus infectivity and the progression of the disease.