It's a genetic luck of the draw. Here is some explanation:
Genetic or immune defects may impair ability to fight Covid-19.
Genetic or immune defects may impair ability to fight Covid-19. A significant proportion of patients who develop life-threatening forms of Covid-19 have genetic or immunological defects that impair their ability to fight the virus, research has found. The Covid Human Genetic Effort international consortium describes two glitches in severely ill Covid-19 patients that prevent them from making a frontline immune molecule called type 1 interferon. The patients would have carried these glitches for years before the pandemic, or in the case of the genetic errors, all their lives. The discovery may help to explain a mystery surrounding the coronavirus: why it leaves some sufferers sick or dying in intensive care, while others remain barely affected or asymptomatic.
Defects in early immune responses underlie some severe COVID-19 cases.
COVID-19 kills some people and leaves others relatively unscathed. But why? Age and underlying health conditions are risk factors, but scientists are trying to tease out other differences, including in people’s genes or immune systems, that may play a role. Two new studies show that flaws in the body’s early response to viral infection, one caused by genetic defects and one by traitorous immune responses, are behind some severe COVID-19 cases.
In one study, published online September 24 in Science, researchers identified certain genetic defects in some people with severe COVID-19 that make the body produce fewer interferons, proteins that are part of the immune system’s early warning system. In other people with severe disease, however, the body’s own immune responses disable interferons, a second study published online in Science the same day finds.
Covid-19 scientists flag key immune function as a turning point in life threatening cases.
Genetic analysis of Covid-19 patients published in the same journal revealed two dozen gene mutations that had been “silent” until patients were infected by SARS-CoV-2. Researchers -- many of them also involved in the antibody study -- sequenced the genomes of 659 patients with life-threatening cases of the disease; 3.5% carried genetic variations that inhibit interferon production. Those genetic flaws were similar to the ones that Hoischen and his colleagues from a dozen Dutch centers described in the Journal of the American Medical Association two months ago. The two sets of brothers had inherited a gene mutation that impaired the interferon response, keeping their immune systems from fighting the coronavirus until it had replicated for days. You don't get to choose your parents.