Scientists are studying all the information that has been collected about Covid-19. What exactly did they find out, and will this knowledge be enough to stop the pandemic? Apparently not. This virus even kills young people. Why this happens, they do not know. Therefore, it is risky to conduct experiments on young volunteers in order to accelerate the creation of a vaccine.
Coronaviruses have long been creating a lot of problems for humanity. Some of them cause the common cold, but recently two fatal types have emerged: severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).
But amid the Covid-19 pandemic and worldwide chaos, their impact has faded. In just a few months, the new coronavirus has quarantined dozens of countries and claimed more than 100,000 lives. And the disease continues to spread.
This is an extraordinary achievement for a spiky ball of genetic material with a diameter of 80 billionths of a meter, coated in fatty chemicals called lipids. Humanity was put to shame by a very modest enemy.
On the other hand, our knowledge of Sars-CoV-2 - the virus that causes Covid-19 - is also outstanding in its own way. Five months ago, this organism was unknown to science. Today it is a subject of study on an unprecedented scale. Vaccines are being developed, antiviral drug trials have begun, and new diagnostic tests are emerging.
So the questions are clear: what have we learned over the past five months, and how will this knowledge help end this pandemic?
Where did the virus come from and how was it first transmitted to humans?
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Researchers are almost certain that the Sars-CoV-2 virus originated in bats, which have a strong immune response to viruses. Therefore, viruses multiply faster in order to somehow bypass it. We can say that bats are a kind of reservoir of rapidly multiplying and easily transmitted viruses. When viruses are passed from bats to other mammals whose immune systems are slower, they multiply rapidly. Most of the evidence suggests that Sars-CoV-2 was transmitted to humans through "intermediaries" like pangolin lizards.
“Most likely, the virus jumped from a bat to another animal near a person. Perhaps it happened in the market, says Professor Edward Holmes, a virologist at the University of Sydney. - And therefore, if this animal is a carrier of the virus from a bat, then there is a high probability that it will be transmitted to the person who deals with it. Then this person goes home and infects his family, and this is how an outbreak occurs.
How does the virus spread and how does it affect humans?
Particles infected with the virus enter the body and come into contact with the cells lining the throat and larynx. They have a large number of receptors on their surfaces - known as Ace-2. (Cell receptors play a key role in transferring chemicals into cells and triggering signals between them.) "This virus has a surface protein that blocks this receptor and injects its RNA into the cell," says virology professor Jonathan Ball of the University of Nottingham.
Once inside, the RNA is inserted into the cellular replication mechanism and produces multiple copies of the virus. They break out of the cell and the infection spreads. In response, the immune system produces antibodies, which in most cases stop its development.
"Covid-19 infection is usually mild, and this is, one might say, the secret of the virus's success," adds Ball. "Many do not even notice that they are sick and continue to go to work and the supermarket, infecting others."
Unlike Covid-19, SARS (which is also caused by the coronavirus) is much more acute and kills one in ten. In most cases, the sick are immediately admitted to the hospital, and this helps to stop further infection - the transmission chain is interrupted. Covid-19 is milder and often does without hospitalization.
Why is the coronavirus fatal in some cases?
However, the virus sometimes causes serious complications. This happens if it travels down the airways and infects the lungs, where there are even more cells with Ace-2 receptors. Many of these cells are destroyed and the lungs fill up with remnants of dead cells. In these cases, patients require treatment in intensive care.
Worse, in some cases, the immune system is overloaded - immune cells rush into the lungs to attack the virus, and inflammation occurs. This process sometimes gets out of control, more and more immune cells are infused, and inflammation intensifies. This phenomenon is called a cytokine storm. (In Greek, "cyto" is a cell, and "cinema" is movement). In some cases, this is fatal.
Why a cytokine storm occurs only in individual patients, and not in the vast majority, is still unknown. According to one version, some Ace-2 receptors are more vulnerable to coronavirus attacks than others.
Does immunity appear in those who have been ill?
Observing convalescent patients, the attending physicians find in their blood a fairly high level of neutralizing antibodies. These antibodies are produced by the immune system and coat the invading virus at specific locations to prevent it from entering cells.
“It is clear that the immune responses to Covid-19 are increased in those affected,” explains virologist Mike Skinner of Imperial College London. "And the antibodies generated by the immune response will provide protection against future infections - but it should be noted that this is unlikely to be protection for life."
Most virologists agree that immunity to Covid-19 will only last a year or two. "It goes well with other coronaviruses that infect humans," Skinner said. - This means that even if the majority eventually become infected, the virus can still become endemic, that is, there will be seasonal peaks of infection. And then the situation regarding Covid-19 will stabilize."
In short, the virus will stay with us for a while. But what will happen to his sickness? Some researchers suggest that it will become less deadly. Others believe that it can mutate and then, on the contrary, its lethality will increase. Skinner hesitates. “Let's look at the pandemic from the perspective of a virus,” he says. “It is spreading rapidly around the world. He is fine. There is no point in mutating."
Only an effective vaccine will save us from coronavirus once and for all, Skinner said.
When will the vaccine appear?
On Friday, Nature magazine reported that 78 vaccine projects have been launched worldwide, with 37 more in development. Among the ongoing projects is the Oxford University vaccination program, which is now in the first stage of trials. Two more are being developed by American biotech corporations, and three more by Chinese scientists. Other vaccine developers say they plan to begin human trials later this year.
This prompt response gives hope that a vaccine against Covid-19 can be developed in a very short time. However, vaccines require large-scale safety and efficacy studies. Thousands of people will receive the vaccine and others will receive a placebo. This will help determine if the vaccine has helped prevent natural infections. This is a long process.
Some scientists have suggested a way to speed it up - to deliberately expose volunteers to the virus to determine the effectiveness of the vaccine. "This approach is not without risks, but will potentially help speed up testing of a promising vaccine by many months," said Nir Eyal, professor of bioethics at Rutgers University.
Volunteers are looking for young and healthy volunteers, he stresses: "Their health will be closely monitored, and they will have access to intensive care and all the necessary drugs." The fruit of these efforts could be a vaccine that will save millions of lives - because it will appear much faster than one that passes all three stages of standard trials.
But deliberately infecting people - for example, the same volunteers who will receive a placebo vaccine - is controversial. “You have to think carefully about everything,” says University of Bristol professor Adam Finn. - Young people may volunteer, but this virus sometimes kills even young people. Why this is happening, we have not yet figured out. However, the third stage of testing is still far away, so we have time to think it over carefully."
Robin McKie