Saturday, June 25

The mystery of those immune to covid: some people have avoided contagion and we still don’t know how

Everything indicates that the worst of the Covid pandemic has already passed in Spain, despite the fact that the disease continues to cause hospitalizations and deaths. However, two long years have passed in which we have had to learn to live with this virus. And after this long time in which more than 12 million infections have been registered in Spain, there are still people who have managed to avoid the infection, or at least the disease caused by SARS-CoV-2. How have they achieved it?

How many people have gotten rid of Covid?
In the first place, it must be taken into account that the number of registered Covid cases is not an adequate indicator to estimate how many people have been spared the contagion. The 12.24 million cases indicated by the statistics would imply that 26% of the Spanish population has suffered from this disease, but this figure includes some people who have been infected several times, while ignoring many who infected and whose contagion was not recorded in the statistics. This includes many asymptomatic infections.

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The last major serological study carried out by the authorities was carried out before vaccination of the disease began, in December 2020, and estimated that almost 10% of the population had suffered from the infection.

More recent studies indicate the growth of the figure in the last year and a half. The authors of an analysis of seroprevalence in the Valencian Community indicated that the data they obtained (50%) could be extrapolated to the rest of Spain. Estimates from the European Commission indicate instead that the proportion of Europeans infected at some point would be higher, between 60 and 80%.

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Asymptomatic cases or people who have never been infected.
This discrepancy between the figures is due to the nature of the data itself, different things are measured, but also due to the fact that many people have gone through the infection without suffering from the symptoms of the disease. We all know someone who has not suffered from Covid but who has had to take tests regularly, few can say they have never been infected by the virus.

We do not know why.
However, although we do not know for sure how many there are, we do know that there are people who have not been infected either symptomatically or asymptomatically. What we do not know is why, how they have managed to avoid the virus during these two years of pandemic. Queen’s University Belfast researcher Lindsay Broadbent tried to answer this question recently in an article for The Conversation.

The first intuition is that these people have not been exposed to the virus. Many people have taken precautionary measures against the virus to the extreme, it is true, but these measures cannot explain the number of people not infected. After 26 months of the pandemic, many people have “lowered their guard” without being infected afterwards.

However, this explanation contrasts with people’s experiences. There are known cases in which individuals have been infected without even knowing when and cases of close contacts in which there has been no infection.

There are an infinity of factors that affect and that we would link to luck: the viral load, characteristics of the space that surrounds us, air currents… That is why there is little that we can be sure of.

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The vaccines.
It is true that many people have “lowered their guard” after vaccination, and this could be an important factor. Again, vaccines can only be partially responsible for this phenomenon. Vaccines are known to have a high success rate in preventing severe cases of Covid but their ability to limit infections is less.

But again, Broadbent indicates in his article, vaccines cannot fully explain this phenomenon, since the entry of omicron further reduced the ability of vaccines to prevent SARS-CoV-2 infection.

Are there other explanations?
In Broadbent’s article, the researcher points to other possible explanations. In it she talks about the possibility that the relevant factor is in the cell receptors. In this case, the virus would enter the body of these immune people but would not be able to enter the cells to multiply and unleash a chain reaction.

University of Birmingham immunologist Zania Stamataki agrees in pointing out this possibility in an article for The Guardian. In it she explains the possible role of ACE2 proteins, which may help explain why children are less vulnerable to this disease.

Another possibility that Broadbent addresses would have to do with the immune response. It is known that the response of this defense system has a lot to do with the symptoms of the disease, but its rapid and effective action could in theory nip the spread of the virus in the human body at the root.

But why only some people?
There are three factors to consider. The first of these has to do with lifestyle, healthy habits should have some impact. The article gives sleep as an example, not getting enough sleep could condition the body’s ability to ward off infections.

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The second aspect to take into account according to Broadbent depends less on us, and that is genetics. Genetics is known to be related to the appearance of serious Covid symptoms. It is therefore plausible that genetics is behind these processes in which the body gains the upper hand against infection.

It is foreseeable that efforts in this direction will give us more clues about the interaction between genetics and vulnerability to Covid, although it may be useful later to face future epidemics.

The third explanation could come from outside our body. About 200 types of coronavirus are known, although the variants that are known to affect humans do not reach 10. Four types of coronavirus are in fact the cause of 30% of colds.

From the early stages of the pandemic, there was speculation about the possibility that colds caused by these viruses could cause immunity against Covid. The key could be, according to some experts, in the T lymphocytes, key cells in the immune system responsible for protection against viruses and other organisms.

For Broadbent this is a possibility, although he also points out that it contrasts with the rate of reinfection of Covid, which allows several infections to be possible within a year.

Both Stamataki and Broadbent conclude their articles with a call for caution, in the words of the latter “it is sensible to continue taking precautions against this virus about which we still know so little.”

Image | Anna Shvets at Pexels

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