From the first weeks that scientists began to study the impact of the new SARS-CoV-2 coronavirus on human health, one of the first observations made was that the lethality of COVID-19, the respiratory disease caused by the coronavirus, it increased progressively with age.
The information provided by NYC Health + Hospitals, a New York City health institution, on the distribution of death cases by age points to such progressiveness, accentuated if the patient in question suffers from an adjacent disease, known as comorbidities.
In the upper graph prepared by Wodlrometers, with data updated as of May 13, it is observed how as age increases, so does the fatality rate of the virus, with the risk of death being much higher in cases of adjacent diseases, among These include diabetes, lung disease, cancer, immunodeficiency, heart disease, hypertension, asthma, kidney, liver disease, and obesity.
Therefore, older people are also the most vulnerable to the coronavirus, and not because they are more easily contagious, which seems to remain uniform at all ages; But because they are at higher risk of suffering a COVID-19 with serious complications and even death.
But why is this so? What makes an immune system more vulnerable to COVID-19? The answer is multiple and complex. There are several factors that can make adults more vulnerable to COVID-19. Guillermo Quindós Andrés, professor of Medical Microbiology at the University of the Basque Country, points out to Very Interesting what these factors are.
Immunosenescence
The first is obvious, but it does not offer a single, simple and absolute explanation: the immune system also ages , as do all the cells and organs of the body. This is how Quindós explains it: “With age, our immune system deteriorates, like any other organ; it is what we call immunosenescence, the aging of the immune system ”. A natural defensive system of the older organism also implies less efficient responses. And a poor or inefficient immune response helps the coronavirus win the race. Of course, as we anticipated at the beginning of the paragraph, there are no absolute answers. As Quindós recalls, there is great variability between some people and others ”. That is to say, there is also a genetic component involved in the health of our immune system, or in the ability to keep it young for longer, as would occur with other areas of the human body. “Some older people have a defensive response that many young people would envy,” acknowledges Quindós.
General health
Recent studies have shown how the coronavirus affects many organs in the body. A complete analysis of the journal Science recently analyzed the progression of COVID-19 in hospitalized patients, observing the involvement of different organs: from the lungs, through the liver, the heart and blood vessels, the kidneys, the intestines, the eyes and even the brain. These damages cause unsuspected symptoms in a respiratory disease , such as diarrhea, kidney and / or liver failure, conjunctivitis, altered smell and taste, drop in blood pressure, thrombosis, and even strokes. Although only 5% of patients globally suffer serious alterations like these, in absolute numbers it is not a negligible figure.
It is not so much age that is associated with the risk of suffering these serious alterations as general health, because young people can suffer from adjacent diseases, as we mentioned at the beginning of the article, comorbidities. But, as Quindós reminds us, what is also true is that an older organism predisposes to a worse functioning of the organs, which makes them more vulnerable to these complications.
“With age, not only does the immune system age, but also all other organs. When we grow up, we accumulate diseases that have nothing to do with infectious diseases, but that can favor them ”, he explains.
Any previous illness can aggravate some type of infection, even if it is a respiratory illness. For example, diabetes. Quindós continues as follows: “Any endocrine alteration, as occurs in diabetes, alters the immune system because it causes alterations in phagocytosis (the capacity by which the immune cells engulf other cells involved in the elimination of pathogens); on the other hand, a circulation problem can prevent the ‘arrival’ of the defensive response to all parts of the body. Another example: many proteins are synthesized in the liver that participate in the immune response ”, the microbiologist illustrates.
And let’s not forget respiratory diseases, such as COPD (Chronic Obstructive Pulmonary Disease). Therefore, we could exclude very few diseases from the list of risks associated with complications of COVID-19: anyone can generate a hostile environment in the body, which means that the body is not in the best possible condition to face the virus. And these conditions naturally worsen with age.
If the coronavirus also negatively intervenes in the functioning of the body’s organs, as we pointed out in the report in the journal Science , the previous poor health would create a very unfavorable scenario , which would further worsen the evolution of the disease, in a kind of vicious circle.
Other conditions that affect the entire population
Angiotesin Regulatory Enzyme 2 (ACE2)
In addition to age, other risk factors are recently being discovered that would make each patient more or less vulnerable to coronavirus infection. An example is angiotesin converting enzyme 2 (ACE2), which has a vasoconstrictor function (which narrows blood vessels), among others. This receptor enzyme also acts as a kind of lock in our cells where the key fits, in the form of the S protein (spike) of the coronavirus.
Previous studies suggested that men appear to have a higher level of this enzyme in their cells, which would make them more vulnerable to the coronavirus. But recently we have learned that it is not so much a matter of quantity, but of quality. ACE2 receptors are highly dependent on the X chromosome. Therefore, it is suggested that women’s receptors (XX) are more efficient or, rather, that their regulatory function would be more preserved in women , to the detriment of men ( XY). However, more studies are still needed to determine this question with greater confidence.
Cross immunity
Another of the most interesting conclusions, which has recently come to light in the journal Cell , is that the fact that people have previously faced another coronavirus could have generated an immunity that would make them more resistant to COVID-19 .
To understand this, we have to know that there are seven types of coronavirus, that we know of so far, that can affect humans: 229E, OC43, NL63, HKU1, SARS-CoV, MERS-CoV, and SARS-CoV-2. The last three are probably familiar to you from having read their names in the media.
SARS-CoV-1 is the one that caused the 2003 outbreak of Severe Acute Respiratory Syndrome; MERS-CoV caused an outbreak of Middle East respiratory syndrome in 2012; SARS-CoV-2 is our little ‘arch enemy’, which causes COVID-19. And the first four are coronaviruses that cause about a third of common colds . It is likely that you, who are reading this article, have gone through one of them at some point in your life.
Well, what the new Cells study says is that four out of ten people would have immunity against the SARS-CoV-2 coronavirus without having passed it, because many of these viruses have characteristics in common. An organism that has previously experienced a coronavirus infection seems to preserve a certain type of immunity or immune memory that would allow it to deal with the new coronavirus: a certain advantage. This is what we call cross immunity.
This ‘prior’ immunity, on the other hand, would also explain why it is estimated that there are so many asymptomatic or mild cases.
Cross immunity in older people
And we return to the aging factor. Quindós recalls that, with age, this cross immunity is likely to decrease: “ We still do not know how long immunity lasts , but it is likely that a young person who has experienced a coronavirus through a common cold has generated immunity, which a few years later it will allow him to better cope with the new coronavirus ”.
Micro-RNA
Another study published by the Augusta Medical University, in Georgia, points to another favor of ‘lack of protection’ against the age-associated coronavirus: micro-RNA .
Micro-RNA plays an important role in our body in controlling gene expression. In addition, they play a defensive role against viruses: they adhere to them and cut their RNA, the genetic material of the coronavirus, without which it cannot replicate and infect other cells. The conclusion of these researchers is that the micro-RNA that should attack the virus that causes COVID-19 decreases with age, and also due to various chronic health problems already mentioned. This would help explain why older people and people with pre-existing medical conditions are vulnerable to SARS-CoV-2. The study is published in the journal Aging and Disease.
One person, one immune system
Guillermo Quindós, however, insists on pointing out that the variability from person to person for all the conditions that we have mentioned is very strong. A high age may not necessarily imply possessing these vulnerabilities, because it all depends on the general state of health and genetic predisposition.
Of course, the older you are, in general terms, the greater the risk of suffering from all kinds of complications. And COVID-19 is no exception.
