RNA viruses generally have very high mutation rates compared to DNA viruses,[6] because viral RNA polymerases lack the proofreading ability of DNA polymerases.[7] This is one reason why it is difficult to make effective vaccines to prevent diseases caused by RNA viruses.[8]
en.wikipedia.org/wiki/RNA_virus
6. Sanjuán R, Nebot MR, Chirico N, Mansky LM, Belshaw R (October 2010). “Viral mutation rates”. Journal of Virology. 84 (19): 9733–48. doi:10.1128/JVI.00694-10. PMC 2937809. PMID 20660197.
7. Klein DW, Prescott LM, Harley J (1993). Microbiology. Dubuque, Iowa: Wm. C. Brown. ISBN 978-0-697-01372-9.
8. Steinhauer DA, Holland JJ (1987). “Rapid evolution of RNA viruses”. Annual Review of Microbiology. 41: 409–33. doi:10.1146/annurev.mi.41.100187.002205. PMID 3318675.
COVID-19 has already displayed high rates of mutation.
h/t Builder