Research: Why did some people get infected with coronavirus several times, and some not at all?

(Patria) - Although we have all somewhat forgotten about the coronavirus pandemic, the answer to the question of why some people got infected several times and some not even once - has still not been found.

Until now. Namely, scientists are on the verge of solving this mystery after conducting an extensive study.

University College and Imperial College London, along with the Wellcome Sanger Institute, conducted research in which volunteers were exposed to the SARS-CoV-2 virus that causes Covid under controlled conditions, and their reaction was studied in the finest detail, reports Jutarnji list.

The study, published in the journal Nature, involved unvaccinated volunteers with no history of having had Covid.

They were exposed to a small amount of the original strain of the virus via a nasal spray. The volunteers were then placed in quarantine where they were closely monitored and regularly tested, and their samples were analyzed under controlled and safe conditions.

In addition to blood, samples from a total of 16 volunteers were taken from the tissue between the nose and throat. Tests were performed before exposure to the virus and again, at specific intervals, after exposure.

The samples were then processed and analyzed using single-cell sequencing technology, making it possible to extract and analyze the genetic material of each individual cell.

Thanks to this advanced technology, the development of the disease could be tracked in great detail from the pre-infection phase to recovery.

Despite the volunteers being exposed to exactly the same dose of the virus, not all of them later tested positive for Covid.

Scientists classified the volunteers into three separate groups. Six volunteers developed a typical mild form of the disease and tested positive for Covid a few days after the onset of the first symptoms. This group was named the "persistent infection group".

Of the remaining ten volunteers who did not immediately develop a persistent infection, meaning they somehow resisted the virus in a very early stage, three developed a "medium-term" infection with occasional individual positive tests for the virus and limited symptoms. This group was named the "transient infection group".

The remaining seven volunteers remained negative on all tests and never developed any symptoms. This group was named the "abortive infection group". This is also the first confirmation of abortive infections, for which there was no prior evidence.

Despite the different outcomes, participants in the study from all groups had some specific new immune response, including those whose immune systems prevented infection.

Scientists then measured the time to the onset of the cellular response in all three groups and observed different patterns.

For example, in volunteers where the virus was only briefly detected, a very strong and immediate accumulation of immune cells in the nose was observed just one day after infection.

Something completely different happened in the persistent infection group, where a delayed immune response was observed, starting only about five days after infection, which allowed the virus to establish itself in the body.

In these individuals, cells stimulated by a key immune response were detected in both the blood and the nose. This response, called the "interferon response," is one of the ways our body signals the immune system to fight viruses and other infections.

Surprisingly, the response was first detected in the blood and only then in the nose, suggesting that the immune response from the nose spread very quickly.

Finally, in volunteers who did not develop a persistent infection, a specific gene called HLA-DQA2 was detected, which could be used as a marker of protection.

This information could be of great benefit in identifying individuals who are likely to be protected from severe forms of Covid.

This study has significant implications for future treatments and vaccine development and is a very important step towards better preparedness for the next pandemic.