How do Viruses Mutate(Pfizer)

From what has been observed thus far regarding the genetic evolution of SARS-CoV-2, it appears that the virus is mutating relatively slowly as compared to other RNA viruses. Scientists think this is due to its ability to “proofread” newly made RNA copies This proofreading function does not exist in most other RNA viruses, including influenza. Studies to date estimate that the novel coronavirus mutates at a rate approximately four times slower than the influenza virus, also known as the seasonal flu virus. Although SARS-CoV-2 is mutating, thus far, it does not seem to be drifting antigenically. It should be noted, however, that SARS-CoV-2 is a newly discovered virus infecting humans. There are still many unknowns, and our understanding of the SARS-CoV-2 virus continues to grow. This relatively slow mutation rate for SARS-CoV-2 make us hopeful that investigational SARS-CoV-2 vaccine candidates will potentially have one less hurdle toward offering the ability to provide protection over a longer period of time.

Influenza viruses undergo antigenic shift, an abrupt, major change in the virus’s antigens that happens less frequently than antigenic drift. It occurs when two different, but related, influenza virus strains infect a host cell at the same time. Because influenza virus genomes are formed by 8 separate pieces of RNA (called “genome segments”), sometimes these viruses can “mate,” in a process called, “reassortment.” During reassortment, two influenza viruses’ genome segments can combine to make a new strain of influenza virus.

 

https://www.pfizer.com/news/articles/how_do_viruses_mutate_and_what_it_means_for_a_vaccine