https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6107253/
Quote: 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. Researchers often assume that natural selection has optimized the mutation rate of RNA viruses, but new data shows that, in poliovirus, selection for faster replication is stronger and faster polymerases make more mistakes. The fabled mutation rates of RNA viruses appear to be partially a consequence of selection on another trait, not because such a high mutation rate is optimal in and of itself.
RNA viruses ability to rapidly change their genome underlies their ability to emerge in novel hosts, escape vaccine-induced immunity, and evolve to circumvent disease resistance engineered or bred into our crops.
Their inherently high mutation rates yield offspring that differ by 1–2 mutations each from their parent, producing a mutant cloud of descendants that complicates our conception of a genotype’s fitness.
Researchers have suggested that RNA virus mutation rates have evolved to be just under the threshold for lethal mutagenesis (sometimes referred to as error threshold but that selection for genetic diversity and other consequences of a high mutation rate push RNA viruses to near their catastrophic limits.
