Re-infection by new variants isn't conjecture. More and more evidence is emerging that naturally acquired immunity is not very protective for a very long period of time against some of the newer variants.
Brazil is becoming the case study in this, where their entire hospital system is again being overwhelmed -- largely by re-infection.
Many thought a second wave was impossible in Brazil’s Amazon because of the severity of the first. A second crisis has stunned the city of Manaus, reports Luke Taylor , and raises questions around a new variant and the likelihood of natural herd immunity Hospitals in the Brazilian Amazon...
www.bmj.com
While it's still being studied, it is far from being just "conjecture."