▎ WuXi AppTec content team editor
When it comes to COVID-19, many people are afraid to avoid it. In the UK, however, a group of young people have voluntarily contracted COVID-19. This is not a stupid game between young people, but has a serious scientific purpose - to model the infection of the new crown virus in the human body. Today, the results of this study are reported in the form of news in nature magazine, and specific papers are being peer-reviewed in the Nature series and have been uploaded to a preprint server.
As soon as the paper went live, it caused a lot of discussion. This is partly because of the topical nature of the research itself, and partly because there is no shortage of unexpected results in the research.
There is no shortage of controversial research
The researchers mentioned in the introduction section of the paper that the new crown disease is a clinical syndrome caused by the new crown virus, which is very complex in itself. However, research on COVID-19 infection has been conducted in almost all animal models and may not fully reflect the situation of COVID-19 in humans. And globally, many young people have mild or no symptoms after contracting the virus, but they can be an important driver of community transmission. Therefore, it is necessary to model the infection of this group and understand how the infectivity will change over time.
In order to realize this idea, the researchers decided to have selected volunteers infected with the new crown virus artificially, and learn about the dynamics of the virus, immune response, transmission dynamics and other information. In fact, active infection with the virus has not been uncommon in the past. For decades, people have used similar methods to study infectious diseases such as influenza and malaria. Nature's news notes that some researchers believe that conducting such research early in the development of a COVID-19 vaccine could help accelerate vaccine development. Others, however, argue that effective treatments were barely available in the early stages of an outbreak, where little was known about the virus. Therefore, it is difficult to justify the risks posed by the study.
The study is also covered in detail on the nature website, see references for details[2]
But tens of thousands of volunteers still choose to join. After careful selection, a total of 36 volunteers joined the study. They are up to 29 years old and 18 years old, in good health, and are at low risk for COVID-19. Moreover, none of them had been infected with COVID-19 before and had not been vaccinated. The study's design was approved by a British ethics committee, and all volunteers signed informed consent forms. After recruitment, two volunteers had serum transformations and were therefore excluded from the study. In the end, 34 volunteers received the coronavirus infection. They were compensated more than £4,500 (about 40,000 yuan) and were placed under quarantine observation at a hospital in London.
A new discovery of COVID-19 infection
Because the harm and long-term risks of the coronavirus have not been elucidated at the time of the study, the scientists used a very low dose to be on the safe side. Nature's news profile says this is roughly equivalent to the amount of virus present in a single respiratory droplet (the virus uses a wild-type virus discovered in the UK in early 2020, not the latest COVID-19 variant). Because this amount was so low, scientists expected to use higher doses of the virus to infect most of the volunteers.
But they were wrong.
Studies have found that even at such low doses, more than half of people are still infected with COVID-19. Of the 34 people, 18 passed the PCR test and showed positive for COVID-19. After only 40 hours (1.67 days) of infection, shedding of viral particles can be identified by throat swab detection and qPCR. This is much faster than nasal swab testing, which takes 58 hours (about 2.4 days).
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This finding refreshes the perception of COVID-19 infection. The Nature report also points out that the current epidemiological results suggest that there is an incubation period of about 5 days from potential exposure to the virus to the onset of symptoms. This study shows that these volunteers can test positive and develop symptoms within 2 days of infection.
The researchers also found that in infected people, viral loads began to rise rapidly, peaking at 112 hours (about 4.7 days) and 148 hours (about 6.2 days) at the throat and nose, respectively. Interestingly, although the virus can be detected first in the throat, the viral load in the nose is much higher than in the throat. At most 12 days after infection, the researchers were also able to detect active viruses from the volunteers.
The symptoms of the volunteers were not severe
In the 2 to 4 days after the infection, the volunteers' symptoms began to become obvious, but most of them were mild respiratory symptoms, such as sore throat, runny nose, sneezing, etc., 7 people developed fever (above 37.8 degrees), but none developed a persistent cough. This finding may be important because one of the hallmarks of COVID-19 disease, traditionally thought to be a persistent cough, does not match the findings. In addition, the time node when the volunteers' symptoms were most severe coincided with the time node at which the viral load peaked in the nose. But despite the overlap in time, the researchers did not observe a direct correlation between the two — whether the viral load was high or low did not appear to affect the severity of symptoms.
Image credit: 123RF
In addition to respiratory symptoms, loss of taste or smell is a very common phenomenon: about 70% of infected people experience this experience. And in line with the common sequelae of the new crown, 5 infected people still have these symptoms after 6 months, and 1 case of symptoms lasted even more than 9 months.
The study also revealed an interesting phenomenon - some volunteers had a high viral load and a long duration of the virus, but they did not have any symptoms. Researchers have a variety of explanations for this, one is that they have been infected with other coronaviruses that cause the common cold in the past, thus becoming immune to the new coronavirus, and the other is that their innate immune system is inherently strong, so it can resist the new crown infection. "Why is it that someone who has not been exposed to a similar virus can still be protected? We are understanding the root causes behind it. Professor Christopher Chiu, the head of the study, said.
Limitations and other considerations
"This is a potentially important advance for future vaccine and drug development." Professor Miles Davenport, an immunologist in Australia, said he was not involved in the study. He pointed out that the findings of this study allow us to study the body's immunity in a more controlled environment. Some scientists also mentioned that the study appeared to be safe and well executed. Similar studies or trials in the future should be reassuring.
Other researchers expressed concern about the health of the volunteers because the study used a virus that did not weaken the virulence, and more than a quarter of the volunteers experienced a prolonged loss of smell or taste after infection. This impact should be better measured. Others question the importance of research because it doesn't bring enough scientific or social benefits, and the risks are somewhat unworthy in comparison. The authors also mentioned in the discussion session of the paper that the small sample size of this study is also one of the limitations.
However, in summary, the authors mentioned at the end of the abstract that as the first human attack on the new crown virus, no serious safety signals were observed, and the adverse reactions of volunteers were expected. The study also supports twice-weekly rapid testing sufficient to make a diagnosis before 70 to 80 percent of viable viruses develop in response to potential viral spread.
We also hope that under more scientific exploration, scientists can have a fuller understanding of the new crown virus, help overcome the epidemic as soon as possible, and let the world return to its original appearance!