On Being Asymptomatic with COVID-19: How?

Environmental & Science Education, STEM, Health, Medicine, History of Science, Nature of Science.

Ed Hessler 

The corona virus--SARS-CoV-19--is brand new to us (other corona viruses are not, e.g., the common cold). It was described as "novel" because it was the first time it had been found in humans. and something new seems to be learned about it, especially its effects on some of our major body systems. It is proving to be a significant challenge to scientists to puzzle out why.

Another puzzle is the number of people with corona virus who show absolutely no symptoms--the only range I've seen (see below) is from 30.8% to 94.6% with the CDC estimating the rate at about 40%). I think about this when I'm asked at a clinic whether I've been in contact with anyone who has had a positive test or COVID-19. I wonder about those I may have been in contact with who have the virus.

Reporting for the Washington Post (available as part of free daily updates and series on COVID-19), Ariana Eunjung Cha discusses the research and some ideas on why some are protected. Is it the amount of the exposure (called the inoculum) or genetics or could it be that some people already have partial resistance.

With respect to the latter, researcher Monica Gandhi who specializes in infectious diseases at the University of California-San Francisco, “'A high rate of asymptomatic infection is a good thing. It’s a good thing for the individual and a good thing for society.'”

 Here is the hypothesis which Cha describes as "mind-blowing."  It is "bolstered by a flurry of recent studies.  ... [A] segment of the world’s population may have partial protection thanks to 'memory' T cells, the part of our immune system trained to recognize specific invaders. This could originate from cross protection derived from standard childhood vaccinations. Or, as a paper published (August 4 Science) suggested, it could trace back to previous encounters with other coronaviruses, such as those that cause the common cold.  The article is technical but completely accessible on-line.

Cha's article is deservedly long, chock full of details, and includes a percent chart which summarizes testing studies from around the world of people who tested positive for the coronavirus but had no symptoms, and two short videos: one on what antibody tests can teach us about potential coronavirus immunity, and the other on how the virus is such a master of disguise. 

The details Cha provides are important in another respect for they describe quite a bit about the nature of science, e.g., the work of teams with various interests and expertise, the use of history in science, and how threads of evidence are being pieced together to provide evidence that supports, rejects or modifies  hypotheses.