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Covid-19 pandemic. Coronaviruses have been causing health problems for a long time. Several versions are at the origin of common colds, and in recent years, two types have created epidemics that result in many victims: severe acute respiratory syndrome (SARS) and Middle Eastern respiratory syndrome (walking).
But its impact was much less, compared to the global disaster unleashed by the new coronavirus. In just a few months, Sars-CoV-2 has quarantined dozens of countries and has resulted in more than 120,000 deaths worldwide. And the disease continues to spread.
Scientists’ knowledge of Sars-CoV-2, the virus that causes COVID-19, is remarkable. This was an organism unknown to science five months ago. Today it is under study at an unprecedented level. There are numerous vaccine projects, antiviral studies have been launched, and new diagnostic tests are emerging.
So what have scientists learned in the past five months and how could this pandemic end?
Where the coronavirus came from and how it infected people
The researchers discovered that Sars-CoV-2 was almost certainly bats, which developed strong immune responses to viruses. These reactions make viruses reproduce faster so that bats’ immune systems can penetrate. This makes the bat a rapidly growing and highly transmissible reservoir of viruses. Then, when these viruses pass to other mammals, which do not have an immune system with such a rapid response, the viruses immediately spread to their new hosts. Most of the evidence suggests that Sars-CoV-2 began infecting humans through an intermediate species, such as the pangolin.
“This virus probably passed from one bat to another animal, and the other animal was probably close to people, perhaps in a marketplace,” says Professor Edward Holmes, a virologist at the University of Sydney.
“And if the animal has a bat virus and a human interacts with it, there is a good chance that the virus will spread to the person who interacts with the animal.” Then that person will go home and transmit the virus to another person, which will cause an outbreak, “explains the professor.
How coronavirus is spread and how it affects people
Sars-CoV-2 is transmitted through the virus-containing drops that are cleared by an infected person who coughs or sneezes.
The particles are inhaled and come into contact with the cells that cover the throat and larynx. These cells have a large number of receptors, known as Ace-2 receptors, on their surfaces. Cellular receptors play a key role in the penetration of chemicals into cells and in activating signals between cells. “This virus has a surface protein that binds to that receptor and introduces its RNA into the cell,” says Professor Jonathan Ball of the University of Nottingham.
The researchers believe that people can become infected with the coronavirus more than once. What effects would the vaccine really have?
Once inside, that RNA enters the cell proliferator and makes several copies of the virus. They leave the cell and the infection spreads. Antibodies generated by the body’s immune system eventually attack the virus and, in most cases, stop its spread.
“An infection with Covid-19 is generally mild, and this is really the secret of the virus’s success. Many people don’t even know they are infected and continue to go to work or the supermarket and infect others,” says Ball.
When the new coronavirus becomes lethal
Although most cases are mild, the virus can sometimes cause serious problems. This happens when it moves through the respiratory tract and infects the lungs, which are even richer in cells with Ace-2 receptors. Many of these cells are destroyed and the lungs are congested. In these cases, patients can seek intensive care.
Worse still, in some cases, a person’s immune system is mobilized, attracting cells to the lungs to attack the virus, causing inflammation. This process can spiral out of control as many immune cells overflow and the inflammation worsens. This is known as the cytokine storm. (In Greek, “I quote” means cell and “cinema” means movement). In some cases, this can kill the patient.
It is unclear why cytokine storms occur in some patients, but not in the vast majority. One possibility is that some people have versions of Ace-2 receptors that are slightly more vulnerable to coronavirus attacks than most people.
Are we immunized for life if we have been infected?
Doctors who examine patients recovering from a Covid-19 infection find fairly high levels of neutralizing antibodies in the blood. These antibodies are produced by the immune system and cover an invasive virus, preventing it from entering cells.
“It is clear that immune responses against Covid-19 are created in infected people,” says virologist Mike Skinner of Imperial College London.
“And the antibodies created by this response will provide protection against future infections, but we must keep in mind that this protection is unlikely to be for life,” he added.
Most virologists believe that immunity to Covid-19 will last only a year or two.
“It is the same as other coronaviruses that infect people.” This means that even if most people end up exposed to the virus, we are likely to have seasonal spikes in infection. We will reach an equilibrium state in terms of Covid-19, “says Skinner.
In short, the virus will remain with us for a time. But could it change its virulence? Some researchers have suggested that it could be less deadly. Others said it could be mutated to be more deadly. But Skinner doubts it.
“We have to see this pandemic from the point of view of the virus as well. It spreads all over the world, it works well. The change does not bring any benefit,” he says.
When will we have a vaccine?
Eventually, an effective vaccine will be developed that will free us from the threat of Covid-19, says Skinner.
Nature magazine announced Friday that 78 vaccine projects have been launched worldwide and another 37 are under development. Some of them are in fairly advanced stages. This remarkable response raises hopes that a Covid-19 vaccine can be produced in a fairly short time. However, vaccines require long-term, large-scale efficacy and safety studies.
As a result, some scientists have suggested a way to speed up the process, deliberately exposing volunteers to the virus to determine the effectiveness of a vaccine.
“This approach is not without risk, but it has the potential to speed up vaccine testing for many months,” says Nir Eyal, professor of bioethics at Rutgers University.
Volunteers must be young and healthy, he said.
“Their health would also be closely monitored and they would have access to intensive care and any available medications,” adds Eyal.
The result could be a vaccine that could save millions of lives if it is ready to be used in a much shorter time than a vaccine that has gone through all the usual stages.
But deliberately infecting people and giving placebo to some as part of the testing process is a controversial practice.
“It just caught our eye then. Young people can volunteer for such a process, but it is a virus that also kills young people. We don’t know why yet. However, there is still some time left until this testing phase, so that we have time to carefully analyze the idea, “says Professor Adam Finn of the University of Bristol.
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