SARS-CoV-2 Human Challenge — What Do The Study Results Tell Us?

Aditi Bhargava
5 min readFeb 15, 2022

Researchers at the Imperial College of London performed a unique and a much-needed study. The authors should be commended for this work and for publishing these findings. The participants must be commended as well for their courage. We should keep in mind that this valuable data and insight would not have been possible if these individuals were vaccinated.

Whether the results will be ignored or considered and guide changes in COVID-19 policy and vaccination mania, time will tell.

Thirty-six (36) healthy volunteers aged 18–29 years with no prior evidence of COVID-19 infection or vaccination were exposed intranasally to a bolus of wild-type SARS-CoV-2 virus (GBR/484861/2020). See study design below. Only 18 of the participants became “infected”, whereas 16 people did not have any detectable virus or any symptoms and were called “uninfected”. Two participants were excluded as they naturally became infected between recruitment and before they could be exposed to the virus in controlled settings. Despite being exposed to large amounts of purified virus from an infected individual, only ~53% (18/34) of the people developed mild COVID-19. These finding closely recapitulates the real-world data, where a significant subset of people despite being exposed to the virus, never develop symptoms or disease, the so-called asymptomatic people.

Screening, exposure, and recruitment of individuals for Human Challenge Study
Clinical study design for up to 28 days post SARS-CoV-2 exposure in people.

The infected developed mild COVID-19

Loss of smell (anosmia) and poor sleep quality (dyssomnia) was reported by 67% of the infected participants (12/18). Running nose, stuffiness, and headaches were the most common and frequently reported symptoms. Interestingly, the researchers did not find any association between viral load and symptom severity and high viral load was also seen in asymptomatic individuals. Viable virus (virus that can be cultured and grown) from symptomatic people could be recovered for up to 10 days after exposure, but not from individuals who did not get infected. All “infected” individuals were quarantined in individual negative pressure (will not allow any aerosol to escape) rooms in the hospital…



Aditi Bhargava

Dr. Aditi Bhargava is a molecular neuroendocrinologist with research focus on sex differences in stress biology and immunology.