How can it be explained that all your relatives or even people who were together shortly before they found out they had the disease have been infected with the coronavirus, but you remain “unaffected”?
It's a question we ask more and more often, but there is a scientific explanation.
There are three factors that lead to the “protection” of certain individuals from the coronavirus.
Danny Altman, a professor of immunology at Imperial College London, told CNBC that studies show that the chances of someone becoming infected in a household when there is a case “are not as high as you might think”.
What happens to those “who never get stuck”
In particular last month, a new study was published by Imperial College London, suggesting that people with higher levels of T-lymphocytes (a type of cell in the immune system) from common cold coronaviruses were less likely to be infected with SARS-CoV-2. , the virus that causes COVID-19.
Dr. “Exposure to the SARS-CoV-2 virus does not always lead to infection and we have tried to understand why,” said Ria Kountou, who led the study.
“We found that high levels of T cells produced by the body when infected with other coronaviruses, such as the common cold, can then protect against COVID-19 infection,” he said.
However, he warned that “although this is an important discovery, it remains just a form of protection and I want to emphasize that no one should stand alone in this. On the contrary, the best way to protect yourself is to be fully vaccinated, that is, to have done the boosting dose “.
Lawrence Young, a professor at the University of Warwick, told CNBC on Wednesday that “there is a great deal of interest in cases of 'never catching a coronavirus', that is, people who have not been infected, even though they have come into contact with a household case.” their”.
Natural immunity from previous infections
According to the professor, the data suggest that these individuals have acquired natural immunity from previous infections with coronaviruses of the common cold.
About 20% of common cold infections are due to common cold coronaviruses, he said, “but why some people maintain cross-immunity levels remains unknown.”
It is also noted that in addition to the immunity offered by coronavirus infections, another factor that may affect why some are more “sensitive” than others, is the COVID-19 vaccination.
The role of vaccines
Coronavirus vaccines have been shown to reduce serious infections, hospitalization and death and remain largely effective against known variants of the virus. However, they are not 100% effective in preventing infection and the immunity they provide decreases over time, and has been undermined by the Omicron variant.
Cardiff University professor Andrew Freeman says some people catch COVID-19 and others do not “possibly related to immunity from vaccination, previous infection or both.”
“We know that many people are still infected with Omicron (usually with mild symptoms) despite being vaccinated. However, vaccination still reduces the chance of infection and the immune response varies from person to person. “Thus, some are infected and some are not, despite the very significant exposure to the virus,” he notes.
As he adds, “certainly cross-immunity from previous infections with a common cold probably plays an important role, especially if the individual also has protection against vaccination.”
The genetic factor
Another question that has arisen during the pandemic is why two people with COVID-19 may respond so differently to the infection.
One may have severe symptoms, for example, and the other may be asymptomatic.
The answer may lie in the genes
According to Professor Altman, according to research conducted by other experts on immunogenetics (the relationship between genetics and the immune system) and coronavirus infection, differences in each immune system “play an important role, at least in whether one develops symptoms or not”.
This research focuses on different human leukocyte antigens (HLAs) and looks at how they may affect one's response to COVID-19.
“The basic genes that control the immune response are called HLA genes. They are important for the response when someone comes in contact with SARS-CoV-2. “For example, people with the HLA-DRB1 * 1302 gene are significantly more likely to have symptoms,” he said.
FILE PHOTO: A nurse prepares a fourth dose of coronavirus disease (COVID-19) vaccine as part of a trial in Israel, at Sheba Medical Center in Ramat Gan, Israel December 27, 2021. REUTERS / Ronen Zvulun / File Photo
What research has shown that deliberately infected people
The professor also highlighted the first results of a British human trial conducted by Imperial and other researchers, in which 36 healthy young adults were deliberately exposed to the coronavirus, but only half of them became infected.
Of the 18 volunteers who became infected, 16 developed mild to moderate cold symptoms such as runny nose, sneezing and sore throat.
At the same time, among the 18 infected participants, the mean time from initial exposure to the virus to its detection and early symptoms (i.e., the incubation period) was 42 hours.
After this period, there was a sharp increase in the amount of virus (viral load) detected in smears received from the nose or throat. These levels peaked on average about five days after infection, but high levels of infectious virus continued to be collected in laboratory tests for an average of up to nine days after vaccination and up to a maximum of 12 days for some.
Finally, it was interesting where the highest concentration of the virus was found. While the virus was detected first in the throat and earlier than in the nose (40 hours in the throat compared to 58 hours in the nose), virus levels were lower and peaked earlier in the throat.
Maximum levels of the virus were significantly higher in the nose than in the throat, indicating a potentially greater risk of the virus being eliminated by the nose than by the mouth.