The SARS-CoV-2 transmission riddle - Part 10

Human challenge studies of respiratory virus transmission

In previous instalments, we examined the properties of respiratory viruses. In Riddle 6, we broadly described the part played by challenge studies in understanding causality and transmission. We also described the evidentiary rules based on previous work updated in light of the significant advances in gene sequencing and molecular epidemiology. We now begin to apply these rules to the research evidence for the pandemic agent SARS-CoV2.

Researchers following empirical methods prefer controlled experiments to observations. Controlling the selection of participants, viruses, time to infection and signs of it ensures the isolation of participants and other aspects that make the experiment more robust, meaningful and credible.

The experiments on human transmission take the name of challenge studies (or Controlled Human Infection Model - CHIM), to which we have already alluded. Challenge studies have a history stretching back at least to the smallpox experiments of Edward Jenner over 200 year…