Healthy, young people who were intentionally exposed to SARS-CoV-2 developed mild symptoms—if any—in the world’s first “human-challenge” study of COVID-19. Such trials present a unique opportunity to study viral infections in detail from start to finish, but are controversial because of the risks they pose to participants.
Researchers intentionally exposed 36 people aged 18-29 with the original SARS-CoV-2 variant via nasal droplets. Two of the 36 were found to have developed antibodies between screening and inoculation, so they were excluded from most of the analysis. That left 34.
Of those, 18 (53%) tested PCR positive, 17 (50%) of them with symptoms and one without. This means 16 (47%) never tested positive, despite being exposed via lying on their back for 10 minutes with a blob of SARS-CoV-2 infected snot up their nose.
This raises serious questions about what constitutes infection, as all participants had been thoroughly exposed to the virus with half resulting in no symptoms or PCR positivity. Interestingly, there was no correlation between symptom severity and viral load, measured both using Ct values from a PCR test and viable virus.
The results were posted on February 1 on the preprint server Research Square and have not been peer reviewed.