Scientists conducted the world’s first challenge study using SARS-CoV-2. The experiment carried out by the scientists was published on the server of the “Nature Portfolio Journal” before the scientific review. Who took part in it and what are the results of the study?
- 34 participants took part in the study, of which 18 eventually fell ill. In addition, 16 had symptoms classified as mild or moderate. None of the participants had severe disease
- Throat and nose swabs were collected twice daily and virus activity was assessed using PCR and laboratory tests
- Regardless of the severity of symptoms, all of the infected study participants had more or less similar levels of the virus in their bodies
- “We are trying to understand the basics of why people are protected even though they have not been exposed to such a virus before” — Dr. Christopher Chiu of Imperial College London explained
- More information can be found on the Onet homepage
The study began in the first quarter of 2021, when researchers at Imperial College London set out to deliberately infect a small group of volunteers (this type of experiment is called challenge studies). Due to the dangers of the type of research, the ethics committee had to approve it in the first place.
Provocation studies have been used for decades to study influenza, malaria and many other infectious diseases. However, they are often faced with a lot of negative opinions, emphasizing the danger to which the participating patients are exposed.
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The course of the study
Only young, healthy people who had not been subjected to COVID-19 and had not been previously vaccinated were qualified for the study. Additionally, participants had to demonstrate good overall health. Ultimately, 34 people aged 18 to 29 took part in the experiment.
First, the volunteers were tested for anti-COVID-19 antibodies to make sure they had not been exposed to the coronavirus before. A droplet containing a small amount of active virus was then injected into their nose. For this purpose, a variant of the coronavirus that preceded the variant Alpha (B.1.1.7) was used. This mutation is considered to be more contagious with SARS-CoV-2.
The concentration of virus in this drop was comparable to the concentration of the pathogen in a drop taken from the nose of an infected person at the time when it is most infectious. Following the administration of the virus, the volunteers were carefully monitored, so they spent the next two weeks at the Royal Free Hospital in London.
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Scientists’ conclusions
The most common symptoms that occurred in the patients followed were typical of other respiratory infections: sore throat, runny nose and sneezing. The fever was less common, while the persistent cough that became the hallmark of COVID-19 did not develop in anyone. Out of 34 participants, 18 eventually fell ill, 16 of whom had mild or moderate symptoms.
Thirteen infected people lost their sense of smell, in 13 of them the sense of smell returned to normal within three months. In three people, however, the olfactory disturbances lasted longer. Some people did not develop any symptoms, but their upper respiratory tract had as much virus as the symptomatic participants, and their infections lasted just as long. As no one in the study group became seriously ill, the results are considered representative only for mild COVID-10 cases.
The mean incubation time of the disease, i.e. the time from exposure to the virus until it is detected in the body, was 42 hours. The researchers also observed that the virus concentration increased rapidly after incubation until the first symptoms appeared. About 40 hours after exposure, the virus could be detected in the throat and around 58 hours in the nose, but it was in the nose that the virus peaked earlier.
The highest virus concentration was observed on the fifth day after exposure and its activity in the nose was maintained for 10 days. An interesting observation, however, was the fact that, regardless of the severity of the symptoms, all infected participants in the study had more or less similar levels of the virus in the body. Throat and nose swabs were collected twice daily, and virus activity was then assessed using PCR and laboratory tests.
In an interview with Nature magazine, Dr. Christopher Chiu, an infectious disease physician and immunologist at Imperial College London who led the study, admitted that his goal was to understand why so many people did not get infected even though they were exposed to SARS-CoV-2. Additionally, some uninfected participants had very low levels of the virus for a short time, suggesting that their immune systems were actively fighting it.
The scientist also emphasizes that in the course of future research, the participants of this experiment will try to explain why this happened. Previous research has suggested that the coronaviruses that cause colds may protect some people against the COVID-19 virus. Another possibility is that some people have a strong innate immune response that does not require prior encounter with a particular pathogen or closely related virus.
“We are trying to understand the basics of why people are protected even though they have not been exposed to such a virus before” — Chiu explained.
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