Critiquing the Sars-CoV-2 Human Challenge Experiment


Critiquing the Sars-CoV-2 Human Challenge Experiment

Written by Daniel Roytas (MHSc Human Nutrition), BHSc (Naturopathy), Dip. RM

A paper titled “Safety, tolerability and viral kinetics during SARS-CoV-2 human challenge in young adults”1 was recently published in Nature Medicine, one of the most prestigious medical journals in the world. In this experiment, young healthy volunteers were supposedly exposed to the Sars-CoV-2 virus. Many people claim that this paper is proof that the Sars-CoV-2 virus does indeed exist and is the cause of the disease known as Covid-19. This blog post will examine the methodology and results of this paper to elucidate whether or not it actually proves viral causation of disease.

In this experiment 36 volunteers between the age of 18-30 with no previous history of infection or vaccination against Sars-CoV-2, were exposed to the Sars-CoV-2 virus1. The virus was inoculated (syringed) into the nasal cavities of the participants, who then laid supine for 10 minutes and then sat upright for 20 minutes with a nose clip to ensure the virus had “maximum contact time with the nasal mucosa”. Within a few days following exposure to the virus 18 (53%) participants became infected and 16 (43%) remained uninfected. Infection was confirmed via polymerase chain reaction (PCR) and the symptoms of both infected and uninfected groups were recorded.

Virus Isolation

The first question that must be addressed is how was the virus being used in this study actually isolated? The paper mentions that a nose/throat swab was taken from a single patient supposedly infected with Sars-CoV-2, however no other details are provided regarding the isolation and purification techniques. The authors state that they used the same protocol as the International Severe Acute Respiratory and Emerging Infection Consortium Coronavirus Clinical Characterisation Consortium (ISARIC4C)2. Upon revision of the protocol ISRCTN66726260 outlined by ISARIC4C, they merely state that the infectious agent is “grown in a laboratory”. The specific details about this process of growing the virus were not apparent.

The fact that the methodology used to “isolate” the virus is not readily available is concerning. Without this information it is impossible to know precisely what the volunteers were being exposed to. In order to prove cause and effect, there must be an independent variable being assessed. To date, every single human or animal challenge experiment in the field of virology has attempted to infect healthy hosts with toxic cell cultures3,4. Virologists have never exposed healthy hosts to just isolated and purified viral particles taken directly from a sick host. Instead, they take mucous from a sick person, add it to a cell culture containing monkey kidney cells and various other toxic substances before starving the cell culture of nutrition3,4. When the cells in the culture start to die, this cytopathic effect is said to be caused by the “virus”. Toxic cell cultures contain many different sources of genetic material (monkey kidney cells, foetal bovine calf serum, horse blood etc) and other toxic substances and are therefore not an independent variable. In other words, to prove X causes Y, you must first have X. Nowhere in this paper has it been shown that scientists had X to begin with. Therefore, it is impossible to draw the conclusion that the volunteers became sick because of a “virus”.

Diagnosing Infection

In this study, infection was determined via PCR, however the validity of the PCR test has been called in to question because it is not fit for diagnostic purposes5. The accuracy of the PCR is reliant on the primers that are being used. Primers are short sequences of DNA which hybridize with DNA in the sample. The PCR can only work when the primers directly match sequences of genetic material of the thing you looking for. It is well known that the PCR primers for Sars-CoV-2 were developed without an isolated virus and were instead created via guess work, assumptions and computer modelling5,6. In addition to this, because the Sars-CoV-2 virus was never isolated away from all the other genetic material after being grown in a cell culture, it is likely that the PCR is providing false positive results (ie the PCR is matching with our own genetic material and not a virus)5,7. The diagnosis of disease from a “positive” PCR test is clinically meaningless in the absence of other signs and symptoms.

No Control Group

Nature is supposed to be the most prestigious scientific journal in the world. How is it possible that a study such as this one, which lacks a control group, is suitable for publication in such a journal? The presence of control groups is important because it allows researchers to confirm that study results are due to the manipulation of independent variables rather than extraneous variables8. Without a control group it is basically impossible to draw any reliable conclusion from the experiment.

A control is essential to detect whether people were actually becoming infected from a “virus” or if they were falling ill from other factors. Why didn’t the scientists utilise a control group in this study? It truly is an incredible oversight. This could have been done rather simply, by recruiting a group of healthy volunteers and exposing them to an inert saline placebo. Without a placebo, we will never know if people were falling ill because of the experimental process itself or other external uncontrolled factors.

In this experiment both infected and uninfected people developed symptoms, which suggests people were falling ill for reasons other than being infected with a “virus”. It is well known that exposing healthy people to saline results in the development of cold and flu like symptoms9. There is also evidence to show that people develop colds and flus after having insect powder sprayed up their nose10. Therefore, how do we know the symptoms experienced by the “infected” participants are being caused by a “virus” and are not the result of having something sprayed inside their nasal cavity? Without a control group, it’s impossible to know.

Lack of Blinding

In addition to not having a control group, this study also failed to blind the participants. Blinding participants is important in scientific experiments because it accounts for the nocebo effect. The nocebo effect relates to a person’s negative beliefs or expectations relating to an intervention they are receiving. In the context of this study, every single participant knew they were being exposed to the virus and therefore would have expected to fall ill. The nocebo effect is incredibly powerful and must be accounted for. This oversight must be addressed, especially when recent data suggests that 75% of all Covid-19 jab side effects are attributable to the nocebo effect11.

On one hand, scientists want to blame the majority of jab adverse side effects on the nocebo effect, but then turn around and imply that the nocebo effect is not important enough to account for when experimentally infecting people. Without the participants being blinded, how do the authors know that 75% of all symptoms experienced by the participants in this study weren’t a result of the nocebo effect? There is documented scientific evidence of people developing cold and flu symptoms after believing they had been exposed to a virus, when in fact they had been exposed to an inert placebo12. Why didn’t the authors blind their participants? If they used two control groups, one blinded and one unblinded, they could have accounted for the nocebo effect. Given the lack of blinding, the results of this paper are questionable.


How is it possible, that such a highly infectious and deadly virus only infected 18 out of 36 people after being directly syringed into their nasal cavities? Of those individuals who became infected, why were the overwhelming majority of symptoms mild? We are told that the most common symptoms of Covid-19 are fever, cough, shortness of breath and a sore throat. Of the 18 participants who became infected, less than half developed a very mild or “just noticeable” fever or cough. Do these symptoms really indicate a person became infected? It has been known since as early as the 1930’s that people can convince themselves they are sick and can produce symptoms similar to a cold or flu. The following is a quote from a paper published in 1930 in the Journal of Experimental Medicine “It is very easy for an individual who is being used for a transmission experiment to believe that he has a mild cold although objective evidence is extremely slight or absent. Where, as in the beginning of our work, volunteers believed that we were trying to produce colds, they were self-convinced occasionally that they were suffering from a mild infection12.

Furthermore, not a single infected person developed shortness of breath (supposedly a hallmark symptom of Covid) or chest tightness. What is even more interesting is that none of the participants developed severe disease, none required hospitalisation or admission to ICU. The authors also fail to explain why participants who did not become infected actually became ill. How is this possible? Is Covid a highly infectious deadly disease or not? Once again, is the mere act of spraying a toxic substance into a person’s nasal cavity, or telling them they are being infected with a highly infectious and deadly virus, enough to make them sick? The authors cannot answer this question because they did not have a control group, nor did they blind the participants.

Unrealistic Methodology

In no way, shape or form, does the methodology in this experiment reflect natural routes of infection. Growing a “virus” in a toxic cell culture, spraying it into a person’s nasal cavity and then clamping their nostrils shut whilst they lay on their back, is not even closely reminiscent to how a virus is said to infect a healthy host in nature. Why has no experiment ever been conducted for Sars-CoV-2, where people who are sick with the illness (from a natural infection) are exposed to healthy people in controlled conditions? Such an experiment should be done before any other type of experiment in order to prove a natural route of human-to-human transmission is even possible. These very experiments have been done for many diseases like the Spanish flu, chicken pox, measles and Scarlett Fever, however all attempts failed to infect healthy people.


Many people might think that this scientific paper proves Sars-CoV-2 causes disease. Upon closer investigation, this paper isn’t truly scientific in that it does not assess an independent variable, the methodology is not clear so that the experiment can be replicated by others, there is no control group and none of the participants were blinded. Given these obvious and apparent oversights, it’s practically impossible to make any definite conclusions in relation to the results published in this paper.


  1. Killingley B, Mann AJ, Kalinova M, et al. Safety, tolerability and viral kinetics during SARS-CoV-2 human challenge in young adults. Nature Medicine. Published online March 31, 2022. doi:10.1038/s41591-022-01780-9
  2. Semple C, Hardwick H. Clinical characterisation protocol for severe emerging infection. ISRCTN.
  3. Engelbrecht T, Koehnlein C, de Harven E, Bailey S, Scoglio S. Virus Mania: How the Medical Industry Continually Invents Epidemics, Making Billion-Dollar Profits at Our Expense. 3rd ed. Books on demand; 2021.
  4. Cowan T, Fallon S. The Contagion Myth. Skyhorse; 2021.
  5. Borger P, Malhorta B, Yeadon M. Corman Drosten Review Report. Corman Drosten Review.
  6. Corman VM, Landt O, Kaiser M, et al. Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR. Eurosurveillance. 2020;25(3). doi:10.2807/1560-7917.ES.2020.25.3.2000045
  7. Khmelinskii I, Stallinga P, Woodcock L. Role of exosomes in false-positive covid-19 PCR tests. The Lancet (pre-print). Published online 2021.
  8. Control Groups. In: The SAGE Encyclopedia of Communication Research Methods. SAGE Publications, Inc; 2017. doi:10.4135/9781483381411.n94
  9. Robertson RC, Groves RL. Experimental human inoculations with filtered nasal secretions from acute coryza. Journal of Infectious Diseases. 1924;34(4):400-406. doi:10.1093/infdis/34.4.400
  10. Long P, Doull J. Etiology of Acute Upper Respiratory Infection, (Common Cold). Exp Biol Med. 1930;28(1):53-55.
  11. Haas JW, Bender FL, Ballou S, et al. Frequency of Adverse Events in the Placebo Arms of COVID-19 Vaccine Trials. JAMA Network Open. 2022;5(1):e2143955. doi:10.1001/jamanetworkopen.2021.43955


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