In support of my conclusions, observe that Mexico, Central America, and the north of South America are seeing healthy co-circulation of VOC's that are antigenically distant.  Delta is not stomping out these VOC's; it is at about 50% prevalence there, and has little representation in the rest of South America.  B.1.621, Kappa(B.1.617.1, which has a markedly different S protein than B.1.617.2), and P.1.x are growing steadily.  Mexico has just set a record for new weekly and monthly cases.


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Delta took over in the US much more quickly and thoroughly, probably because we had much lower prevalence of the other strains than they did at the beginning(B.1.621 emerged in Colombia) and more import from overseas, even though we're more vaccinated(Mexico is at 22% fully vaccinated).  We might expect even greater expansion of those strains here over time.  You can watch the relative percentage of sequenced strains since Delta's export by zooming the map and pressing the play button on the linked page.

 
It's as though the other strains as just going about their own business as usual as if Delta didn't even exist.  They will continue to be slow to replicate until they mutate, but their R0 is already plenty high for transmission, even with current mutations and vaccinee sera.  It just won't strike like a lightning bolt like B.1.617.2.x or a recombination would; it would be more of a, I hate this hackneyed term, flattened(but greatly elongated) wave.  Then something Delta-esque pops out again once protection via infection wanes, and assuming no highly infectious mutations occur, then Delta strikes again once protection from its infection wanes.

In effect, it'll be two or more pandemics overlaid on top of each other, although "more" is probably later than this winter.
 
In the long term, it will be a race between how fast new serotypes can develop and how fast we can develop and distribute effective polyvalent vaccines.  We lost the race with the first generation of vaccines badly under circumstances where the virus had much less of an advantage than it does today.  Our logistics for vaccine distribution, particularly for the developing world and for boosters, have to dramatically improve for us to win the race, but we plausibly could if there is an optimal number of serotypes that can co-exist, it becomes harder to evolve new ones, and OAS isn't too bad.  Dengue Fever has 4. Rhinovirus has 99 known ones.
 

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