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For now, attempts to understand what the body’s defenses look like in people who have already recovered from Covid-19 have raised more questions than answers.
It is unclear whether all the people who survived the Sars-CoV-2 coronavirus carry antibodies to neutralize it. Even among those with such antibodies, it is not known how long protection will last.
Much of this uncertainty can be explained from the perspective of the theory of evolution. Although other types of coronaviruses tend to cause common and mild forms of the cold, Sars-CoV-2 had no history of living with the human species as it has just invaded the world population of another host’s Homo sapiens.
This means that no human being had specific natural defenses against the virus when he started infecting people in China in late 2019. “Previous infections caused by the other more common coronaviruses are highly unlikely to provide any protection. They belong to groups so distant from Sars-CoV-2 that it would hardly happen “, explains Fernando
Spilki, president of the Brazilian Society of Virology and professor at the University of Feevale (RS).
It is also necessary to keep in mind that most cases produce relatively mild symptoms and uneventful recovery. This means that, even before it can produce antibodies, something that only happens a few days after the beginning of the disease, the organism of many manages to initiate the counterattack to the virus by other means.
Such a reaction is possible because cells have a generic system to recognize viral invaders. One element of this system is the detection of RNA (DNA “molecule” that makes up the genetic material of viruses like Sars-CoV-2) with double strips, says Rômulo Leão Silva Neris, a visiting researcher at the University of California, Davis.
In cells like humans, it is normal for RNA to have a single strand. Captured this molecular oddity, the cell begins to recruit molecules to stop the replication (reproduction) of the virus.
As the days of illness pass, the body finally produces specific antibodies against the virus, generally two types of so-called immunoglobulins, designated by the acronyms IgM and IgG.
When the infection is removed, “knowledge” about how to make the longest lasting IgG antibodies is stored in so-called memory B cells. By coming in contact with the virus again in the future, these cells can trigger the production of antibodies, quickly overcoming the problem.
Two details mess up this relatively simple scenario in the Sars-CoV-2 case. “Some studies have shown that between 20% and 30% of patients who recovered have no detectable levels of antibodies,” says Neris.
Furthermore, what is known about other coronaviruses suggests that this viral subgroup is not very immunogenic, that is, it does not produce as robust a response to the body’s defense system as other invaders, Spilki recalls.
In general, coronaviruses that cause common colds generate transient immunity, which disappears in about a year.
Alternatively, people recovering from Covid-19 may produce antibodies, but some tests have been done after recovery. In this case, the levels of these molecules would be very low in the body and, therefore, more difficult to detect, says Nayara Pereira, a master’s student in immunology at the Institute of Biomedical Sciences at USP and a member of the initiative in Covid Verified line, which verifies the scientific information on the pandemic. .
In addition to questions about how the virus interacts with the immune system, there is still uncertainty about the proportion of people whose body has had contact with Sars-CoV-2.
For now, the only consensus is that, even in the places most affected by the pandemic, the population is still a long way from achieving what is generally called collective immunity, a scenario in which the percentage of people who have already been infected and healed is high enough to serve as a “shield” for those who have not yet had the disease.
Preliminary antibody test results vary, and many have not been officially published in scientific journals, which may decrease their reliability.
Furthermore, the data published so far has been obtained locally rather than nationally, and does not always relate to a sample of people who is representative of the general population.
The highest number so far has come from Chelsea, a Boston suburb, where doctors from Massachusetts General Hospital identified antibodies to Sars-CoV-2 in 31.5% of the 200 bystanders who donated blood in a corner.
A city of 12,000 inhabitants in Germany, in which 500 were analyzed, would have shown a prevalence of antibodies in 14% of the population, while other places in Europe and the USA. USA They have numbers ranging from 1% to 4%.
The only large-scale study conducted in Brazil so far, coordinated by researchers from the Federal University of Pelotas (RS), estimated that only 0.13% of the state’s population would have developed antibodies against the virus.
In tests like these, it is always necessary to take into account levels of sensitivity and specificity. A very specific test is one that rarely produces false positives (that is, identifies the presence of the infection when, in fact, it did not occur); On the other hand, highly sensitive tests produce few false negatives (that is, they rarely indicate that someone who had the infection did not actually have it).
In any case, another point on which scientists agree is that there is no magic formula to “boost immunity”, for example, no food is capable of doing it alone. “What strengthens immunity is a set of factors: balanced diet, adequate sleep, physical exercise and avoiding stress, although in the current situation the last element is more difficult,” says the researcher from USP.
