Scientists infected volunteers with COVID-19 - here's what they found

The aim of the study was to see exactly what happens in the body from the moment of exposure to COVID-19 and until recovery.

 Test tubes labelled "COVID-19 Omicron variant test positive" are seen in this illustration picture taken January 15, 2022.  (photo credit: REUTERS/DADO RUVIC/ILLUSTRATION)
Test tubes labelled "COVID-19 Omicron variant test positive" are seen in this illustration picture taken January 15, 2022.

Researchers have taken healthy people and intentionally infected them with coronavirus, just to see what happens to them.

At face value, for most of us who have been trying for two or so years to do everything we can just to not get infected, this seems like a bit of a strange decision, but the truth is that this experiment is of great scientific importance and many are awaiting its results.

The initial findings from the experiment were published on the preliminary platform Springer Nature, an open platform for sharing research before it is published in established journals and undergoing peer review.

The aim of the study was to see exactly what happens in the body from the moment of exposure to COVID-19, until recovery and its eventual dispelling from the body. For the purpose of the study, the researchers recruited 34 healthy and young volunteers aged 18-30 to take part in the experiment. None of them had previously had Covid or had any resistance to the virus, as confirmed through a serological test for SARS-CoV-2 antibodies conducted at the beginning of the experiment for all volunteers.

The experiment began with the insertion of nasal droplets containing the coronavirus particles into the noses of the healthy, antibody free volunteers. The drops contained the average amount of virus particles that can be found in a droplet spray emitted from the nose of a coronavirus patient at the stage of the disease where it is most contagious.

The strain of the virus used by the researchers (the experiment began in mid-2020) preceded the alpha variant, but was still different from the original virus that started the global pandemic because it already carried mutations in the spike protein, which the researchers believe made it more contagious.

34 were exposed, 18 were infected, zero severe cases

Following the exposure to the virus, 18 of the volunteers contracted COVID, of which 16 developed mild-to-moderate symptoms of the disease (sore throat, headache, muscle and joint pain, fatigue and fever). Around a third of the volunteers (13) lost their sense of smell. It was restored for 10 of them within three months of infection, and three still suffered from the symptom for over three months.

Fortunately, to the researcher's relief, "in our study model that intentionally infected young and healthy adults there were no cases of serious clinical morbidity," said Dr. Christopher Cho, lead researcher in the trial and infections disease specialist at the Institute of Infections and Infectious Diseases at Imperial College London. In a statement issued to the media upon the publication of the initial study findings, he said that for this reason, the findings of the study are particularly relevant for mild-to-moderate cases of morbidity.

Among the 18 volunteers who were infected, the researchers found that the average incuvation period of the virus (the length of time that elapsed between the initial exposure and the first time the virus levels in the body were high enough to detect through testing) was 42 hours. The researchers performed COVID tests on the participants twice a day, during which they took samples from both the throat and the nostrils of each person. 

With PCR tests conducted in the laboratory, they calculated the amount of active and contagious virus particles in each of them. Thus, they found that the viral load in the infected increased a rapid rate at the end of the incubation period. The virus can be detected in the throat earlier - about 40 hours after initial exposure, and in the nose, 58 hours after exposure on average.

The researchers also found that the viral load in the infected peaked on the fifth day after exposure, on average. And usually, the viral presence in the throat was lower than that found in the nose of the sick volunteers and peaked earlier before beginning to decline. 

Another interesting finding reported by the researchers was that all participants had quite similar levels of viral load, regardless of the severity of the symptoms they experienced.

At what stage do rapid tests become reliable?

The researchers also tested, in their experiment, the detection ability of rapid antigen tests throughout the stages of the disease. They concluded that these tests were able to reliably detect the virus at the time of the disease, although were slightly less sensitive at onset and at the end - when the viral load is lower. 

In other words, the rapid tests were less likely to come out positive when the virus levels were lower which means that at the beginning and end of the disease they may give a false negative result.

"We found that antigen tests overall were able to produce a correlation with the presence of the virus in the body, as also confirmed by lab tests," said Dr. Cho. 

"If used correctly and repeatedly, and of course by also acting accordingly when they show a positive result, these tests can effectively affect the stemming of the chain of infections," he added.

As stated, these are just the initial findings of the study, and next the researchers intend to delve deeper and examine why some of the volunteers contracted the coronavirus while others did not. 

In addition, they plan to conduct another experiment of intention infection - this time with the Delta variant. They did not specify whether there was a plan to test with the Omicron variant as well, which is the most contagious strain to date and the most dominant at the moment.

"Although there are differences in the level of infection due to the emergence of different variants such as Delta and Omicron, at its foundation it is still the same disease and the same factors will be responsible for protection against it," said Dr. Cho. 

"A new strain can make a difference in terms of the response size, but at the end of the day, we expect that our research has broadly presented the processes that take place in the body following COVID-19 infection," he concluded.