Background: Early-stage interventions in a potential pandemic are
important to understand as they can make the difference between runaway
exponential growth that is hard to turn back and stopping the spread
before it gets that far. COVID19 is an interesting case study because
there have been very different outcomes in different localities. These
variations are best studied after the fact if precision is the goal;
while a pandemic is still unfolding less precise analysis is of value in
attempting to guide localities to learn lessons of those that preceded
Methods: I examine two factors that could differentiate strategy: asymptomatic spread and the risks of basing strategy on untested claims, such as potential protective value of the Bacillus Calmette-Guerin (BCG) tuberculosis vaccine.
Results: Differences in disease progression as well as the possibility of alternative strategies to prevent COVID-19 from entering the runaway phase or damping it down later can be elucidated by a study of asymptomatic infection. An early study to demonstrate not only what fraction are asymptomatic but how contagious they are would have informed policy on nonpharmaceutical interventions but could still be of value to understand containment during vaccine roll out.
Conclusions: When a COVID-19 outbreak is at a level that makes accurate trace-and test possible, investigation of asymptomatic transmission is viable and should be attempted to enhance understanding of spread and variability in the disease as well as policy options for slowing the spread. Understanding mild cases could shed light on the disease in the longer term, including whether vaccines prevent contagiousness.