Some sort of "protection" against Covid-19 infection seems to be enjoyed by those who have a natural defence against the common cold, claim researchers at Imperial College London, but are quick to stress that their finding should not be misinterpreted to mean that anyone who has had a common cold does not get Covid-19.
Besides, this is a small-scale study conducted in 2020, at the beginning of the pandemic and published in the scientific journal Nature Communications, verifying the doctrine of the "ancestral" antigenic sin, which has also been studied in the case of seasonal influenza.
What the British researchers claim
The Imperial College science team focused on 52 people who lived with someone who had become ill with the Covid-19 infection.
Those who had a "stockpile" of certain immune system cells after a common cold appeared less likely to get Covid-19. Experts therefore wanted to answer the question of why some people get Covid-19 after contact with someone who is already sick, while others do not.
Covid-19 is known to be caused by the SARS-CoV-2 coronavirus, while common colds are also caused by other coronaviruses. Scientists have therefore asked themselves whether immunity against one coronavirus can also help protect against another coronavirus.
They focused on the T-cells of the immune system, which play a key role in the body's defence against pathogens.
Some of the T-cells kill all cells infected by a virus, such as the one that causes the common cold. When the person recovers from the common cold, the body builds up a reserve of T-cells as a "memory" of the infection, which are ready at any time to build a line of defence in case of a new attack by the virus.
In the case of the British study conducted in September 2020, the 52 people who had not been vaccinated had no vaccines against Covid-19 available at the time and were living with people who had been diagnosed positive for the coronavirus.
Half eventually caught and became ill with Covid-19 during the 28 days they were under medical supervision and half did not. One-third of those who did not get sick had high memory T-cell levels in their blood. These may have been generated as a consequence of recent infection with another coronavirus that affects humans, perhaps that of the common cold, and thus the protective benefit may be inferred.
However, the researchers are quick to point out that the study should not be misinterpreted and assume that if you have caught a common cold you are also protected from Covid-19, since coronaviruses cause only 10-15% of common colds. The only reliable line of defense against Covid-19 is vaccination.
What is the "original" antigenic sin of coronaviruses
The British study verifies the doctrine of the "original" antigenic sin, which Thomas Francis referred to in 1960 when describing what can happen when a related but not identical microbe infects the body.
As the Professors of the Medical School of the National and Kapodistrian University of Athens (EKPA), Gikas Majorkinis and Thanos Dimopoulos (Dean of EKPA), remind us, after an infection the immune system creates "memory" against the microbe it encountered in the memory cells so that in the next "encounter" it is ready to deal with the microbe faster and more effectively.
Note that this property is exploited by vaccines, creating a "memory" in the immune system, so that when the body is infected it can deal with the microbe more quickly and effectively.
Dr. Francis refers to the case of a related but not identical microbe, as in the case of coronaviruses, which are of the same family but not identical.
"In this case it is possible that because of the relative similarity of the new microbe, the mechanism of initial recognition of the microbes (virgin cells) may not be activated but the memory mechanism (memory cells) may be activated to produce antibodies against the microbe that originally infected the organism. If the antibodies produced have good neutralising power against the new microbe then it will lead to faster and more effective treatment of the infection. However, if the antibodies produced are not as effective against the new microbe then the immune system will be blocked because the processes of primary recognition of the microbe will not proceed adequately. At the same time, the immune memory produces those antibodies that do not effectively neutralize the new microbe, creating vicious cycle conditions," Demopoulos and Mayorkinis explain.
The phenomenon of antigenic "paternal" sin has been studied for several years in influenza. Researchers had shown that prior exposure to specific strains of influenza virus resulted in cross-protection through immunological memory against the 2009 pandemic (H1N1) strains. However, a negative interaction has also been described in different conditions where a previous infection with other types of influenza virus led to an impaired immune response.
The question, then, in relation to the SARS-CoV-2 coronavirus is in principle whether previous infections with widely circulating coronaviruses such as the common cold create conditions of antigenic "progenitor" sin. Secondly, if the memory of the common cold viruses is recalled after infection with SARS-CoV-2, does it work protectively or negatively?
"Some relevant studies show that earlier infection with common cold viruses helps to improve the outcome of the infection by producing antibodies that cross-react with SARS-CoV-2. Another study also showed that infection with SARS-CoV-2 led to an increase in antibodies specific for other coronaviruses without these antibodies having significant neutralising activity for SARS-CoV-2. These could be indications of a negative interaction, but there are studies showing that people who had evidence of recent infection with other coronaviruses recovered more quickly from SARS-CoV-2," they respond.
Source: protothema.gr
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