The existence of Covid-19 and the SARS-CoV-2 virus that causes the disease has been known for less than half a year. And so it stands to reason that the precise pathogenesis hasn’t been fully characterized.

What’s also unclear at this point are reasons for the differential impact the disease has on those who test positive for the novel coronavirus. A neat breakdown into the three categories asymptomatic, mild, and severe cases is far too simplistic.

A Dutch study released this week confirms, for example, that some patients in the “mildly symptomatic” category turn out to be substantially burdened by Covid-19 for long periods of time, sometimes months.