“Another possibility, still speculative but discussed by many scientists in recent days, is that omicron evolved over many months within an immunocompromised patient with a protracted infection. In a patient treated with therapeutics such as monoclonal antibodies or convalescent sera, a viral strain that can survive the assault can potentially amass a host of mutations. Such cases have been documented, but they are not known to have led to outbreaks in the general population.”
Sources?
“Another possibility, still speculative but discussed by many scientists in recent days, is that omicron evolved over many months within an immunocompromised patient with a protracted infection. In a patient treated with therapeutics such as monoclonal antibodies or convalescent sera, a viral strain that can survive the assault can potentially amass a host of mutations. Such cases have been documented, but they are not known to have led to outbreaks in the general population.”
Source:
https://www.washingtonpost.com/health/2021/11/29/how-bad-is-omicron-variant/
This does seem to be a recurring theme—very slow mutation for the most part, and lots of new mutations occurring in immunocompromised “supermutators”.