According to this link, the Dominant Delta Variant may mutate itself into destruction.

The Delta variant in Japan was highly transmissible and keeping other variants out.

But as the mutations piled up, we believe it eventually became a faulty virus and it was unable to make copies of itself.

I was told that evolution was about survival of the fittest, and that in the case of virus strains, a more contagious strain would likely increase in frequency relative to a less contagious one. So how can a mutation of the strain Delta which can't replicate or replicate less, increase in frequency relative to the original Delta strain?

Can a less fit strain of a virus impose over a fitter one?

  • $\begingroup$ Could you clarify what you mean by impose? $\endgroup$
    – user438383
    Commented Nov 27, 2021 at 15:20
  • 1
    $\begingroup$ How are you quantifying 'displaced'? The original strain still exists, presumably, but the other variants are found at higher frequencies. Are you interested in whether it's possible for a less fit strain to reach a higher frequency than another? 'Imposed' doesn't seem to be the correct biological term. I think 'outcompete' is better to use. Sorry if I sound pedantic, but having the correct terminology often is the best way to understand something. $\endgroup$
    – user438383
    Commented Nov 27, 2021 at 15:46
  • 3
    $\begingroup$ If I can simplify the question: “Why would a ‘faulty’ mutated strain of the delta variant increase in prevalence relative to the wild type delta variant?” The answer is probably “it’s complicated” and “more information is needed.” $\endgroup$
    – acvill
    Commented Nov 27, 2021 at 16:58
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    $\begingroup$ Also note that the term “fitness” has a specific meaning in biology. For a given genotype, relative fitness is the proportion of that genotype in the population gene pool of the next generation. So, by definition, a “less fit” strain cannot overtake the wild type. $\endgroup$
    – acvill
    Commented Nov 28, 2021 at 0:30
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    $\begingroup$ @Pablo a less fit strain may outrun a fitter one due to genetic drift, if the infected (sub)population is small... although in this case measuring fitness is problematic. It seems that the variant introduced in Japan, although classified as Delta, had actually low fitness (there is some genetic variation within each variant). Also, a fitter strain may simply become extinct by exterminating all its hosts - not the case of sars-cov-2, but not something unheard of. $\endgroup$
    – Roger V.
    Commented Dec 2, 2021 at 8:59


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