To understand how long immunity to the SARS-CoV-2 coronavirus lasts, a group of Chinese researchers evaluated blood samples from approximately 100 people who were infected with the virus at two different times: six months; and one year after infection. Analyzing the collected material, it was possible to affirm that the immune system maintains significant levels of protection against covid-19 for at least 12 months.
Published in the scientific journal Clinical Infectious Diseases, o preprint — study without peer review — with the participation of researchers from the China Centers for Disease Control and Prevention (CDC). In the survey, both levels of neutralizing antibodies and memory cells—a key component of the immune system—were analyzed.
According to the study authors, the aim was “to understand the characteristics of immunological memory in individuals with different disease severities within one year of disease onset”. In this context, it is possible to affirm, according to the scientists, that “cellular and humoral immunities specific for SARS-CoV-2 are durable – for at least one year after the onset of the disease”.
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Understand the types of immunological memory
To understand the results of the Chinese study, it is necessary to remember that there are two types of immune responses: humoral and cellular. Both are complementary and ensure that the organism is, in fact, prepared for a new battle against covid-19.
When we come into contact with the infectious agent for the second time, the humoral antibodies — from humoral response — are the first defense. Typically, their concentration is usually highest in the first few months of recovery, as the immune system has recently been triggered to produce antibodies capable of fighting the threat that has entered the body. After some time, the number of these antibodies is expected to drop to a baseline level, because the immediate threat no longer exists.
While the level of antibodies declines, the mechanism of cellular immune response. It is this that guarantees that some types of disease only occur once, as usually happens with chickenpox. In the case of covid-19, it is not known how long the immunity will last.
Regardless, the cellular response is like a large file, where the system’s “memories” of all the viruses and bacteria the body has ever come in contact with are stored. It is from this “recollection”, preserved in memory T cells, that the body is able to generate antibodies to protect itself in cases where the coronavirus reappears in the future.
Methodology and results
“We carried out a return visit of six months and one year for 101 patients recovered from the new coronavirus, in order to detect, through multiple tests on serum samples, whether antibodies and immunological memory T cells were still present,” explained the researcher. Liu Jun, one of the study’s authors.
According to the scientists, coronavirus-specific T cells were present in 93% of patients recovered after six months of illness. After 12 months, the specific concentration of this defense cell was little affected, remaining at 92%.
In addition, the study demonstrated that, in more than 95% of recovered patients, specific IgG antibodies can persist for 6 to 12 months after disease onset. Even this higher concentration was related to the higher level of disease severity.
“We also found that IgM antibodies were still detectable in at least 26% of individuals recovered 12 months after disease onset, speculating that the long-term persistence of IgM in some recovered individuals may be one of the immunological features of covid infection. 19, whose mechanism needs to be further investigated,” added the researcher. Now, it is necessary to explore the validity of the finding in larger groups of patients who have recovered from the disease.
To access the full article on human immunological memory against the SARS-CoV-2 coronavirus, published in the journal Clinical Infectious Diseases, click on here.
Source: With information: China
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