Sorry to hear about your friend - I don't mean to minimise the effects of serious cases. I'm referring to the proportion of cases which are asymptomatic or mil

Sorry to hear about your friend - I don't mean to minimise the effects of serious cases. I'm referring to the proportion of cases which are asymptomatic or mild. In some seroprevalence studies asymptomatic reach up to 80%, though it can also be very low. Certainly some younger people seem to have a very bad time with COVID, but that's definitely not universal, suggesting controllable-factors may play a role in their difficulty fighting it off versus their peers, who seem at times to be capable of doing so without issue (rather than this being interpreted as intrinsic to the virus itself, a somewhat greater leap). To take one example - Vitamin D deficiency. This is nearly universal in many modern societies but has a great degree of variance of the deficiency and this is also regional (so, illuminating a possible cause of difference in seroprevalence/asymptomatic studies). Unequivocally, Vit D deficiency is known to be greatly immune-compromising and this increases with degree, being one of the basic building blocks of the human immune system. (It's lead to some questioning if this has been a viral pandemic so much as immune-deficiency pandemic. Which seems a reasonable proposition if indeed there do exist a large percentage of people whom have immune systems apparently capable of easily fighting off COVID.) A good summary of present COVID-19 Vit-D research: https://vitamind4all.org/letter.html https://vitamind4all.org/letter.html