Nature A small subset of infected people spew huge amounts of virus into the air — despite having only mild symptoms.
A study of people who were intentionally infected with SARS-CoV-2 has provided a wealth of insights into viral transmission — showing, for example, that a select group of people are ‘supershedders’ who spew vastly more virus into the air than do others1.
The publication describes data from a controversial ‘challenge study’, in which scientists deliberately infected volunteers with the virus that causes COVID-192. Although the approach drew opposition, the work has now yielded data on questions central to public health, such as whether the severity of symptoms correlates with how contagious people are and whether home COVID-19 tests can play a part in reducing viral spread.
The results highlight how widely and unpredictably disease severity and contagiousness vary between people. “And it’s that variability among humans that has made this virus so difficult to control,” says infectious-disease doctor Monica Gandhi at the University of California, San Francisco, who was not involved in the work. The study, published on 9 June in Lancet Microbe, also suggests that human physiology, not the virus, is to blame for some of the inconsistency of COVID-191.
Design with benefits
Challenge studies are “very bold”, says Gandhi. Some people argue that it’s unethical to give people an infection that can cause severe illness, but the research design comes with benefits. Challenge studies can substantially speed up vaccine testing, and they’re the only way to understand certain aspects of COVID-19, such as the stage before people test positive or develop symptoms.