Since the end of 2019, the new coronavirus has been raging around the world for almost three years. From the original strain to Delta, to Omicron, the new coronavirus has mutated again and again, constantly challenging the fragile nerves of human beings, and has no intention of leaving at all.
In this tug-of-war, have you ever had such a question: why are some infected and some people survived during the epidemic?
advertisement published by the British government for the COVID-19 human challenge trial
In February last year, the UK launched the world's first human challenge trial for the COVID-19 human challenge amid ethical abuse. This highly controversial trial was conducted as follows:
consists of Imperial College London, the British government vaccine task team, the clinical trial research company and other parties to recruit test subjects from the society. To ensure the safety of the subjects, the designers of the trial only select young, healthy people without underlying diseases. At first, 90 people were expected to be recruited, and after 2-3 months of strict screening, 36 healthy young subjects were finally successfully enrolled. These young people are between 18 and 29 years old and are all healthy. They have never received the new crown vaccine , nor have they ever received the new crown .
Image source: BBC NEWS
In the first two days of the test, these 36 subjects were placed in a negative pressure isolation ward for centralized management to prevent virus interference before the test. On the day of the test, the nasal cavity of each subject was injected with live coronavirus, and the pharyngeal swab and nasal swab sampling and analysis were performed every day for the next 14 days, and the antibody levels in the serum were also monitored by blood extraction. These subjects would wear a special mask that was specifically used to collect the air they exhaled. The ambient air in which the subject is located should also be sampled and analyzed. The entire quarantine period was 14 days, followed by another year of follow-up to continuously observe the subject's reaction.
After a series of research, the final results were published in the journal Nature Medicine on March 31 this year. Interested friends can search for the above documents. I briefly summarized the results: Among the 36 volunteers participating in the trial, 18 were infected with the new coronavirus and showed different degrees of symptoms. One was an asymptomatic infected person in , and another 17 people in were not infected from beginning to end. Therefore, there is really a chosen person in the world.
Image source: Beijing News Weibo report
Let's not discuss the ethical issues of the experiment for the time being, these results alone are enough to be shocking. And the most amazing thing is why half of the people were not infected? Did the new coronavirus have eyes?
extends this conclusion to real life and observes it carefully. In fact, similar examples are not uncommon. For example, on the same flight, passengers who are nearing positive cases may not be infected, and some will be infected. Some will be spared; medical staff working in hospital infectious wards are exposed to a high viral load for a long time, and there are still a few people who are actually infected; in a family, parents and children live together for a long time, some will be infected and some will not be infected...
So, what kind of achievements are these chosen people?
What I can think of is that can only be because they have stronger immunity!
To answer this question, we need to understand how the human immune system is fighting viruses?
From a microscopic perspective, the human body's immune system is like a complete set of well-operated and well-trained combat troops, including "outpost warriors" who directly fight against foreign enemies, "post-war organizations" that continuously transport combat forces, and advanced and sophisticated "combat weapons".
virus is a type of microorganism that needs to live in human cells to survive. After leaving the human body, it will not last long in the external environment. Viruses infect humans are actually invading human cells and undergoing adsorption, invasion, proliferation, maturation, and lysis in the cells to cause human diseases. The human immune system can fight viruses by preventing viruses from entering cells, or directly swallowing and destroying viruses that have entered cells. Stop it at all aspects of the life cycle of the virus, inhibit the synthesis of viral proteins, and make it unable to reproduce in the body, and transcribe .
After the virus comes into contact with the human body, it will first be intercepted by a powerful human barrier, which is our skin and mucous membranes. Mucosal epithelial cells can directly sanitize the virus and secrete a large amount of interferon, which is the " rocket " that can help fight the virus. When enough interferon is spread all over the cell, the viruses that are free from the cell will be destroyed.
In addition to physical isolation of the human body, there is also a more powerful set of "antivirus equipment", that is, the innate immune system and adaptive immune system obtained through inheritance, which is what we are born with. The natural killer cells in this set of "antivirus equipment" can, on the one hand, directly or indirectly disintegrate and destroy those poisoned cells that have been trapped by the virus; on the other hand, they can secrete a variety of cytokine , such as interferon, tumor necrosis factor , perforin, etc., further enhance the antiviral effect, destroy target cells, and help quickly clear out of the body.
So, if a person's innate immunity is strong enough and rely on the innate immune system such as the skin physical barrier, mucosal immune system barrier, and natural killer cells with natural killer activity, it can directly block the virus and continue to penetrate the human body. This may explain why the 17 people were not infected.
Image source: CNBC News Report
There is another interesting result in this experiment, that is, the virus sprayed from the nose peaks in the throat earlier, and the detoxification time in the throat is also earlier than the nose, and the nasal position where the virus first comes into contact with it is later.
This is actually related to the nature of the virus itself. Viruses prefer tissues or organs that have strong blood flow and good metabolism in the human body. The throat is a high-quality and livable place with rich blood flow, so the throat is the most vulnerable to virus attacks. But the human body is the greatest design, and the more vulnerable it is to attack, the more perfect the defense system will be.
The throat is connected to the nasal cavity, the left and right connecting the ear canal, and the lower connecting the trachea and lungs, just like a transportation hub.This part is a portal fortress for foreign enemies. There is a tonsil on one side, and tonsils can produce lymphocytes and antibodies. When bacteria or viruses attack, a large number of secreted lymphocytes and antibodies are the first combat force of the traffic fortress, directly participating in the fight against pathogenic microorganism .
Recall, have you ever had a cold in the past when you have had a sore throat, itch, excessive phlegm or redness? That is the lymphocytes or antibodies secreted in the throat are fighting against pathogens!
Under normal immunity, most people will quickly recover through non-medical means such as rest, balance work and rest, and diet management. If you catch a cold frequently throughout the year and cannot resist it with your own immunity, and the disease lasts for 1 or 2 weeks, it is very likely that there is a problem with your immunity, at least the immunity in the throat has already reminded you.
All subjects participating in this trial will receive a reward of £4,500 (RMB 37,500). The organizer said that these remunerations are only used as loss of work and compensation for the work and family life that volunteers were delayed during the experiment, and do not induce young people to participate in the experiment for money.
Just more than two months after the first human challenge test for the new coronavirus, another human drug test was launched in the UK on April 19, 2021. This time, it is to reinfect those who recovered from COVID-19 to explore what immune response can prevent from secondary infection with and how the immune system works during secondary infection. The results have not been published yet, so we will wait and see...
References:
. Killingley, B., Mann, A.J., Kalinova, M. et al. Safety, tolerability and viral kinetics during SARS-CoV-2 human challenge in young adults. Nat Med (2022).
. Edwards, K.M., Neuzil, K.M. Understanding COVID19 through human challenge models. Nat Med (2022).
. Ethical review methods for biomedical research involving humans [J]. Bulletin of the State Council of the People's Republic of China, 2017(27): 44-50.
