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. COVID-19 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 in the early stages to learn lessons of those that preceded them. I examine two factors that could differentiate strategy: asymptomatic spread and differences in use of the Bacillus Calmette-Guerin (BCG) tuberculosis vaccine. These differences point to the possibility of alternative strategies to prevent COVID-19 from entering the runaway phase. The most promising is testing all contacts of anyone who has tested positive, not only those who are symptomatic. Should this demonstrate asymptomatic transmission, then all contacts of anyone who tests positive should be isolated and tested, and only released from quarantine when it is clear that they are past incubation and not positive.
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