by Gisela Gross
It has been proven that millions of people in Germany were infected with SARS-CoV-2 in the omicron wave. Vaccinated, unvaccinated, from infants to the elderly. However, some people have never had a positive test result before. What could be the reason?
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There are many theories…
For the people rescued thus far, it has often seemed like only a matter of time that they contracted corona in the past few months. However, some have resisted the Omicron wave that is currently quelling with millions of infected people across the country, that is, in more than two years of the pandemic, still not knowingly infected with SARS-CoV-2.
If you ask people who belong to the group, you’ll hear a whole host of assumptions about possible causes: Is it possible that long, regular subway rides will become more difficult because you keep getting small amounts of the virus? To predict: “This thesis falls into the realm of speculation,” says Essen virologist Ulf Dittmer.
Other people who are not yet infected are giving themselves good marks for complying with the Corona rules. Some consider themselves lucky simply because they were not infected either from a subsequent positive contact person or from a club visit. Some doubt whether they actually have the virus, just unnoticed and without confirmation. For example, in the days when tests were hardly available. Or when you had symptoms but the tests never worked. It cannot be excluded that this was due to incorrect sampling or timing.
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Why do some people seem uninfected? This is what science says
Scientific approaches to explain the question deeper. However, there is no definitive answer that explains the lack of infection. Alternatively, the key may lie in a combination of different circumstances. “There are some hypotheses that seem plausible,” says Leif Sander, head of the infectious disease clinic at the Charité Berlin.
First of all, one has to take into account that not a large proportion of cases go largely or completely unnoticed. In a public paper from the end of 2021 in “Open JAMA Network,” the authors summarize that even among people with confirmed coronavirus, 40 percent had no signs of illness at the time of testing. The baseline was 100 different international studies with data from a total of about 30 million people.
Against this background, the frequency of testing plays a role in detecting infection. Those who test infrequently are more likely to miss a very mild or asymptomatic infection. With frequent testing, the likelihood of detecting mild cases increases.
Apart from that, genes can also play a role. “There are people who, due to genetic characteristics, can have severe infection with malaria or HIV, for example. To some extent, this will also be the case with SARS-CoV-2,” Sander says. However, genetic factors are not fully understood.
As Ulf Dittmer, director of the Institute of Virology at the University Hospital Essen, explains, the immune system’s genetic makeup – so-called HLA molecules – plays an important role in protecting against Covid-19. Not only did blood groups influence disease severity, but they may also have influenced the transmission of SARS-CoV-2.
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The importance of protection from vaccination is often underestimated: the level of antibodies in the blood, which can make harmless coronaviruses that have penetrated the body, decreases in the period after vaccination. “However, the protection remains great for several months. This also reduces infection,” says Sander.
Immune responses to vaccination also vary from person to person. “If the answer is particularly good, then the combination of vaccination and a previous infection with one of the four common coronaviruses could also play a role,” notes Professor Charity.
Virologist Dittmer says that it is now known that a special subclass of antibodies provides particularly good protection against corona infection. “However, the measurement is complicated, so at the moment no one will know if they have these antibodies or not.”
According to Sander, children have a phenomenon that in general they have a more active innate immune system, so to speak, the immune system is often activated in advance. Additionally, an effect is that people are generally less susceptible to the following underlying pathogens for a few days immediately after infection. This is partly due to so-called interferons, which are mucosal-specific antibodies, which also reduce exposure to Sars-CoV-2 if contact occurs in the time window.
Another conceivable factor: In some people, the immune system may flush the virus out of the body too quickly, Sander says. In a Swedish study, researchers found certain T cells in people who did not become positive after contact with infected family members – a sign that their immune system had definitely coped with SARS-CoV-2, even if there was an infection and also antibodies against SARS-CoV-2 weren’t. The virus can always be detected.”
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Anyone who is not infected yet is not automatically protected forever
What follows? Anyone who thought they were saved so far could actually have the infection behind them. Or they benefited from some temporary effect, such as genetic factors and unknown coincidences. Sander’s conclusion: “The fact that you haven’t had coronavirus before doesn’t mean you’re safe forever. It can look very different with a new viral variant or depending on the situation.” (dpa/dhe)