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expert reaction to a preprint looking at the course of SARS-CoV-2 infection in a COVID-19 human challenge study

A preprint, an unpublished non peer reviewed study posted on Research Square, has looked at the course of SARS-CoV-2 infection in a COVID-19 human challenge study.

This Roundup accompanied an SMC Briefing.


Prof Lawrence Young, Virologist and Professor of Molecular Oncology, Warwick Medical School, University of Warwick, said:

“Human challenge trials have a long history having been used to study infections, treatments and vaccines for many different pathogens ranging from common cold viruses to malaria. These trials provide vital information about the course and dynamics of infection providing insights into virus replication and spread as well as more detailed studies of the body’s immune response to infection and vaccination.

“This is a world first – the first time naïve uninfected individuals have been exposed to SARS-CoV-2 under controlled conditions where the timing of initial infection is known. The study reinforces observations from previous studies of natural infection confirming rapid onset of upper respiratory tract infection after 2 days but shows that high levels of virus are produced in the throat before being detected in the nose. While symptoms were predominantly mild to moderate, peak symptoms correlated with peak virus loads in the nose where high levels of virus shedding were detected compared to the throat. But there was no correlation between the levels of virus shedding and symptom severity. These observations confirm that virus transmission can occur in the absence of significant symptoms emphasising the importance of wearing face coverings over both the nose and mouth. The study also confirms the value of lateral flow testing in identifying those who are likely to be infectious and supports the isolation period of 10 days symptom onset.

“One interesting observation is that only 53% of infected individuals developed PCR-confirmed infection with no obvious differences between the groups. What factors are responsible for this difference are unknown but are likely due to immune factors that will be examined in on-going studies.

“This first report of a human challenge trial with the original SARS-CoV-2 virus paves the way for future studies examining the effect of different vaccines and treatments as well as the behaviour of virus variants.”


Dr Doug Brown, Chief Executive of the British Society for Immunology, said:

“It is exciting to see the results of this study published. This important pre-print provides significant in-depth insights into how SARS-CoV-2 infects the human body and how that infection progresses. This type of study, called a Human Challenge Trial, is where volunteers are exposed to the virus and the course of their infection then monitored in detail. These studies are not easy to carry out and require a lot of resources. However, they provide us with hugely valuable insights into minutiae of disease progression that cannot be obtained through other types of research. 

“This is the first step in developing human challenge studies on COVID-19. While the main aim of this study was to establish a safe and successful protocol to build on in the future, the significance of it should not be underestimated. This study has already generated intriguing insights into the timeline of infection, particularly in the early phase. In the longer-term, the hope is that these findings will now open up a new research avenue to develop a platform that will allow us to speed up the development of new vaccines, antivirals and diagnostics against COVID-19. The UK is a world leader in this type of research that, with the right ongoing investment, will play a significant role in helping us live alongside this virus.”



Preprint title: Safety, tolerability and viral kinetics during SARS-CoV-2 human challenge by Christopher Chiu et al. This work is not peer-reviewed.


All our previous output on this subject can be seen at this weblink:


Declared interests

Dr Doug Brown: “A Trustee of the Association of Medical Research Charities.”

None others received.

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