Variations in cells result in evolution.  For humans,   gene mutations can cause cancer , but might also have beneficial long-term implications.  COVID-19 has been particularly nasty because of mutations, which are called variants. A relatively new term, R-naught, or RO, is more and more being mentioned.  The information below was sent to me with no reference.  It looks generally accurate, but I found a second source,  VOX , which provides some additional details: In short, RO is the number of additional cases caused by an individual so infected.  The original COVID-19 virus had an R0 of 2 or 3, so the 2.7 indicated below is just more specific. VOX indicates that the Delta variant has an RO of 4, but the below quote says 5.7. Measles has an RO of 12. Will future mutations make COVID-19 even worse?  The answer:  no one knows. R naught: the Delta Virus has an R naught of 5.7 versus 2.7 for the original. R naught of other infectious diseases - · 1918 Influenza Pandemic that killed 50 mill