Why are vaccines required for our body's immune system to destroy viruses that cause the likes of Covid-19 or Polio, while viruses that cause the common-cold are self-limiting (go away on their own)? What is so different about viruses that cause diseases requiring vaccines?
$\begingroup$ "..while viruses that cause the common-cold are self-limiting (go away on their own)" You heard of the human immune-system and antibodies - right? But to partially answer your question: Certain strains and their mutations are more 'contagious' and more 'viral' (have a higher virality) than others.. $\endgroup$– iLuvLogixMar 19, 2020 at 14:39
$\begingroup$ "Why are vaccines required for our body's immune system to destroy viruses"...no, vaccines are not 'required' for anything. Most people infected with Covid 19 are recovering fine with no special medicine, so it is self-limiting in most people. $\endgroup$– swbarnes2Mar 19, 2020 at 21:20
$\begingroup$ @swbarnes2 Thanks for the response! Sorry, you're right that a vaccine isn't necessary for the viruses. However, viruses that cause the common cold doesn't cause a pandemic, while the virus that causes Covid-19 does. With relation to the human's immune system, what can be attributed to that difference? I'm sorry if this question sounds silly... $\endgroup$– jyp11711Mar 20, 2020 at 13:29
1$\begingroup$ It's not that polio &c don't "go away on their own" - or more accurately, are defeated by the immune system, it's that they cause lasting damage that persists even after the active infection is controlled. The common cold just causes a bit of sneezing and runny nose, but the polio virus damages nerves. $\endgroup$– jamesqfMar 20, 2020 at 18:24
There is not really an inherent difference between these viruses. Polio is a run of the mill enterovirus - some of its closest relatives are "common colds", while others are less pleasant - see https://www.slideshare.net/TarekMahbubKhan/enteroviruses-and-polio for some examples. Note that some "common cold" viruses have uncommon but nonetheless devastating polio like effects; a leading culprit for acute flaccid myelitis (polio-like paralysis) was the common cold enterovirus D68 ( https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(18)30094-X/fulltext but I haven't checked for updates lately). But for that virus, damaging replication in nerve tissue is at most a rare complication rather than a frequent one.
Coronavirus has long been known for several strains of "common colds"; they were just not as frequently deadly. Unfortunately, we did not see the "cold and flu season" as a demonstration of defenselessness against viral outbreaks, and did not use the opportunity to practice exterminating them.