When I was a medical student doing my pediatrics rotation, our cardiologist fellow came into work one day looking wan and distressed. I asked him what was wrong. Ironically, his young child had been diagnosed with Kawasaki disease, a disease that affects children and can affect the heart. Knowing exactly what the disease was, he was extremely concerned.

Kawasaki is one of many remaining medical mysteries. Striking young children, it causes inflammation of blood vessels. It can affect the blood vessels in the heart and if it does, it can be lethal. The cause is unknown. Most likely, it is thought that an unknown virus infects the victims, the victims develop an immune response to the infection, and the immune response gets misdirected toward the patient’s own tissue.

This is not an uncommon phenomenon. Many pathogens use molecular mimicry to avoid our immune systems. They try to make themselves look like part of our normal body, to evade the defense system.  In the process of clearing the pathogens, sometimes our immune system makes antibodies that end up attacking our own tissue.

We have been unable to find the virus that causes Kawasaki disease. There have been some candidates, including several coronaviruses, but so far it has eluded us.

Given that COVID-19 causes symptoms similar to Kawasaki disease, it is probably likely that Kawasaki is indeed caused by an unidentified coronavirus as well.

Here is my hypothesis: At some point in human history, a new coronavirus leapt to humans, and became established. It is now endemic and almost every single person contracts it at some point, usually when we’re infants. A small sub-fraction of the population then develop Kawasaki disease.

Imagine is the current COVID-19 were to become established across the world and everyone got it as a child. It would be asymptomatic for most people, but now there would be a Kawasaki-like disease in a small number of children.

This scenario is consistent with what we saw with polio, and consistent with my Viral Shockwave Theory. I posit that pathogens, including viruses, that are asymptomatic or mildly symptomatic in children, and can become more virulent in adults, can provide a strong evolutionary advantage to populations of its hosts.