Why did some people not catch the coronavirus?

Why did some people not catch the coronavirus?

The “visits” of the virus became more and more frequent, closer and closer. The coronavirus hit friends, then their children, their grandparents and at some point most of their colleagues. Those who had saved her so far, considered in recent months that it was a matter of time before they also received “visits”. Some, however, also endured the Omicron wave, which in the meantime is receding, infecting millions of people. In short, in more than two years of pandemics, some people have not knowingly become ill or infected with Sars-Cov-2.

If you ask those who belong to this happy group, you will hear a whole range of hypotheses about possible causes. Some attribute this to the fact that they fully complied with the rules of cleanliness and prevention, others consider themselves lucky because they did not come into contact with someone who later became ill or did not become infected in a bar. Others believe they were probably infected but showed no symptoms, especially in the initial period when the tests were absent, or showed symptoms but the tests did not detect coronavirus. Also, the possibility of a sampling error or a timing error cannot be ruled out.

Tests, genes, blood groups, vaccine

Scientific approaches to explaining the phenomenon are deeper, but there is no definitive answer to the question, why some have not been diagnosed with coronavirus. But perhaps the key lies in a combination of many factors. “There are a number of hypotheses that seem plausible,” said Leif Zander, head of the Infectious Diseases Clinic at Charité University Hospital. “First of all, one should keep in mind that a not so small number of infections go largely or completely unnoticed.” In a summary of the end of 2021 published on the Jama Open Network, the authors reported that even in cases of confirmed coronavirus infections, about 40% showed no signs of illness at the time of the test. The basis for this finding was almost 100 different international studies with data from a total of 30 million people. In this context, the frequency of the test plays a role in the detection of infections. Those who do infrequent tests are more likely not to notice a mild or even asymptomatic infection. Because with multiple tests, mild infections are more likely to be detected. In addition, there are genes that may also play a role. “That is, there are people who, because of their genetic characteristics, find it difficult to become infected with the Laveran plasmodium, which causes malaria or the human immunodeficiency virus, HIV,” says Zander. “To some extent this may be the case with Sars-CoV-2. But the genetic factors are not fully understood.”

As Ulf Dietmer, director of the Institute of Virology at Essen University Hospital, explains, the genetic makeup of the immune system, called HLA-compatible antigens, plays an important role in protecting against Covid-19. But blood types have not only affected the severity of the disease, but also the transmission of the virus, it seems. But there is something else that is underestimated, the protection provided by vaccination. The level of antibodies in the blood, which can make viruses and variants that penetrate the body harmless, declines at some point after vaccination. But protection remains and is important for the coming months. “It also reduces infections,” Zander recalls.

“No one is eternally safe”

Of course, the immune response to vaccination varies from person to person. “But when it is particularly good, combining vaccination and previous infection with one of the 4 coronaviruses of a common cold can also play a role,” says the Charité professor. Infectious disease specialist Ulf Dietmar adds to the whole problem that it is known that there is a special subclass of antibodies that provides particularly good protection against coronavirus infections. “But the measurement is complicated, so no one wants to know if they have these antibodies or not.” According to Zander, children generally have a more intensely activated innate immune system, in other words, their immune system is activated before they receive the virus. In addition, people immediately after an infection are generally less susceptible in the coming days to the next pathogenic virus that “hides” in the body. “This is due, among other things, to so-called interferons, specific antibodies to the mucous membrane, which also reduce sensitivity to Covid-19.” Another possible factor, says Xander, is that in some people the immune system can “throw” the virus out of the body very quickly. “In a Swedish study, researchers found specific T cells in people who never became positive after contact with family members who became ill, a sign that their immune system has ‘dealt’ with Sars-CoV-2, even if the infection and antibodies are no longer detectable. “

What is the epitome of all this? Never before the end say someone’s happy. Anyone who thinks he has saved her may have already had a coronavirus. Του his body has benefited from some temporary effects of unknown genetic factors and coincidences. Zander’s conclusion: “Just because you have not been infected in the past does not mean that you are safe forever. A new variant of the virus or a different conjuncture can make the situation completely different.”

DW- Gizela Gross / Irini Anastassopoulou

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