NOT a ELI5 but this should give you a reasonable understanding.
Why are RNA virus mutation rates so damn high?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6107253/
"RNA viruses have high mutation rates—up to a million times higher than their hosts—and these high rates are correlated with enhanced virulence and evolvability, traits considered beneficial for viruses. However, their mutation rates are almost disastrously high, and a small increase in mutation rate can cause RNA viruses to go locally extinct"
Some bloke who was the head of Porton Down aka Public Health England when commenting on the London Plague pits found when digging the tunnel for Cross Rail suggested RNA viruses have a single helix so are prone to high levels of mutations unlike DNA which has the double helix checksum to reduce mutations.
This is probably the episode. https://www.bbc.co.uk/programmes/b04cnps9
How Messenger RNA vaccines work.
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different...
mRNA is not the only solution, some dietary changes can create a chemical based attack vector as your body has evolved to cope with extremes.
This just one example of many different chemical attack vectors.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7413200/
There is also this
https://news.ycombinator.com/item?id=12451198
But I cant find the hacker news link on a paper from MIT which also suggested a 3 day fast reset the immune systems "memory" which was a novel way of wiping vaccine triggered immune system responses and probably isnt what you want to do if you believe in the covid vaccines, but if you are an anti-vaxxer forced into having a vaccine, then it could be a way of wiping its effect from your body if the study was accurate.
Now before you go out fasting, just bear in mind you will be depleting your body of many things like the vampire chemical glutathione (NAC, Glutamine & Glycin) which depletes as you age. Its called the vampire chemical because it whitens skin and makes you sensitive to light amongst other things so there might have been some truth to those vampire legends!
I know Vit D is mentioned alot, the Welcome Trust in Cambridge reversed engineered the human genome back a few years back and suggested there were 2776 Vit D receptors, most concentrated around the immune system genes, but the VDR has a zinc finger so you need to take zinc and both A & D will get you closer to hypercalcemia so that brings its risks, but in 1959 the scientific community did work out if you take A & D you need to take K to mitigate the risk of hypercalcemia. And if you are elderly, you should consider taking taurine as this helps the body manage the fats in your diet (bile) amongst other things, which explains why the elderly generally absorb A & D less easily or respond less to supplementation compared to young people. You'll find taurine in some wacky places in the body.