You're basically exposed to everything during childhood. No prior immunity plus kids are less hygiene conscious, especially in daycares and schools where there's just a lot of contact. Over time our immunities wane, so even if you had Coxsackievirus at a child, you can get it again. Some viruses change (like influenza) and get around preexisting immunity. Or, for example "rhinoviruses", there exist multiple subtypes of the same virus, so you could get type A in one season and type B the next. Finally, some viruses, like coronaviruses, don't really care about preexisting immunity. They tend to create weak immune memory, so you can just get infected over and over. There are definitely examples of virus-virus interactions, for example having RSV somehow protects you from getting influenza for apparently a long time (at least in mouse studies). But I don't know of any study looking at whether covid interacts with a non respiratory virus.
skeeter_wrangler t1_iwurl0v wrote
Reply to comment by [deleted] in Why does hand foot and mouth disease (coxsackievirus) cause blisters in the hands, feet, and mouth? by aubergine_alibi_
You're basically exposed to everything during childhood. No prior immunity plus kids are less hygiene conscious, especially in daycares and schools where there's just a lot of contact. Over time our immunities wane, so even if you had Coxsackievirus at a child, you can get it again. Some viruses change (like influenza) and get around preexisting immunity. Or, for example "rhinoviruses", there exist multiple subtypes of the same virus, so you could get type A in one season and type B the next. Finally, some viruses, like coronaviruses, don't really care about preexisting immunity. They tend to create weak immune memory, so you can just get infected over and over. There are definitely examples of virus-virus interactions, for example having RSV somehow protects you from getting influenza for apparently a long time (at least in mouse studies). But I don't know of any study looking at whether covid interacts with a non respiratory virus.