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Why Does the Same Virus Affect Different People in Different Ways?

Almost a year after the first COVID case, we still don’t know much about it

We know a few things about who is at higher risk of experiencing severe symptoms of COVID-19: The elderly, those with pre-existing conditions pertaining to their heart and lung health and people who are already immunocompromised have tragically comprised the majority of COVID-related deaths and hospitalizations. Yet, many seemingly perfectly healthy people have experienced similar fates. More puzzlingly still, two people with comparable health profiles can catch the virus from the same source, with one experiencing no symptoms while the other needs a ventilator. Exactly why this is, we still just do not know. 

At the moment, all we can really do is speculate. Heart and lung health aren’t entirely straightforward. Someone may pass their annual checkups perfectly, eat well, exercise regularly, abstain from smoking and drinking and yet some rogue little gene they weren’t aware of predisposes them to heart attacks. Meanwhile, someone whose weight and habits may place them into high-risk categories could actually be completely healthy on a cardiovascular level. Basically, there’s always more going on below the surface, and our complicated, expensive health-care system makes detecting the nuances of our health more of a task than most of us can afford. 

But even beyond these physical nuances, the discrepancies in the severity and symptoms of the virus remain a mystery. According to the University of Washington Medicine health site Right as Rain, there are a handful of possibilities experts consider as plausible explanations. One is that some people literally have more of the virus in their system than others. This has to do with both how much of the infection someone may have been exposed to, but more significantly, how quickly the virus replicates within the body. 

The finer details of how and why this might work are still being figured out. An otherwise healthy person’s immune system may not respond strongly enough against the virus when first confronted with it, allowing the virus to reproduce quickly and thus having more severe symptoms. Similarly, an otherwise healthy person’s immune system may over-respond, causing the immune system to actually attack the body. In either case, it may result in someone feeling severely ill. 

While it’s not known for sure, it’s thought that the variances in immune response to the virus is most likely genetically determined. This doesn’t exactly leave us as individuals with much to work with — we know neither the specifics of the genetics that might be at play, nor do most of us know much about our own genes, anyway. 

Again, there remains so much to be uncovered about the virus. The only tried and true way of not experiencing severe symptoms of COVID-19, though, is still just to not get it at all.