Coronavirus: One possibility

There are many possible explanations for why the severity of COVID seems to be declining, and that the case fatality rate is plummeting. These include variations in susceptibility, genetic mutation of the virus, different strains, etc. Another possible explanation is that most of the COVID-19 deaths involved pneumonia. It is possible that the decline in mortality is a consequence of the the decline in pneumonia among those infected with SARS-CoV-2, and that this in turn is a seasonal phenomenon. Perhaps environmental factors in warming weather change the risk of developing pneumonia, and make late spring-early summer infections less lethal. Given that these may contribute to heard immunity, a spike in cases in the summer months, particularly among younger people, may in fact lessen the severity of COVID in the fall and winter.