Darwin and Covid-19

I thought that I had written that so far no one has made the connection between Darwin's survival of the fittest and the various Covid variants: surely each variant that 'catches fire' (the latest being omicron) should proliferate more than other variants - that's why it's the current variant to cause everyone worry. Presumably I had this insight after reading 'The planet of viruses' but I can't see that I wrote it there. Now I remember that I wrote it in a message to my doctoral supervisor after he told me that he had suffered from Covid.

Today I read the following: The mechanism was laid out by Charles Darwin more than 150 years ago: evolution through natural selection. If a person is infected with Covid but mounts a weak immune response, the infection can persist for months. In that time, antibodies neutralise some of the virus, but not the versions they bind to less well. These surviving viruses proliferate, mutate and undergo further selection – potentially leading to variants that evade immune defences. [source] 

One study showed that a particular sample of coronavirus [was traced] to a 36-year-old woman who was not receiving effective antiviral therapy. Tests revealed that she had harboured the Covid virus for 216 days, in which time it accumulated 32 mutations, making it similar to the vaccine-evading Beta variant.

The article goes on to consider that the variants are being established in people with weakened immune systems, such as those undergoing treatment for cancer or for HIV.