Totally not a molecular biologist, virologist, etc.
Influenza is smaller about 13K nucleotides vs 30K for corona, it mutates about 4 times faster. It can maintain its larger genome basically because it has better tech. (It seems to better integrate with what it can find in host cells.)
"We demonstrate here, at the molecular level, that CoVs have indeed acquired an enzyme able to enhance the overall fidelity, and that this event might have directly promoted the jump in size of CoV genomes"
"Well before the discovery of nsp14-ExoN in the large Nidovirales genomes (22), this observation led to Drake’s visionary proposition that “RNA viruses would have to acquire several host genes and adapt them to RNA substrates to achieve a major reduction in spontaneous mutation rate. The result would be a substantial increase in genome size” "
"Specifically, SARS-CoV-2 seems to have a mutation rate of less than 25 mutations per year, whereas the seasonal flu has a mutation rate of almost 50 mutations per year."
Influenza is smaller about 13K nucleotides vs 30K for corona, it mutates about 4 times faster. It can maintain its larger genome basically because it has better tech. (It seems to better integrate with what it can find in host cells.)
"We demonstrate here, at the molecular level, that CoVs have indeed acquired an enzyme able to enhance the overall fidelity, and that this event might have directly promoted the jump in size of CoV genomes"
"Well before the discovery of nsp14-ExoN in the large Nidovirales genomes (22), this observation led to Drake’s visionary proposition that “RNA viruses would have to acquire several host genes and adapt them to RNA substrates to achieve a major reduction in spontaneous mutation rate. The result would be a substantial increase in genome size” "
https://www.pnas.org/content/115/2/E162
https://www.ncbi.nlm.nih.gov/genomes/GenomesGroup.cgi?taxid=...
https://www.ncbi.nlm.nih.gov/nuccore/1798174254
"Specifically, SARS-CoV-2 seems to have a mutation rate of less than 25 mutations per year, whereas the seasonal flu has a mutation rate of almost 50 mutations per year."
https://www.livescience.com/coronavirus-mutation-rate.html