The emergence of three different 501Y variants in 3 different continents may reflect intense selective pressures towards immunity evasion rather than improved transmission. Those with weakened immune systems are less able to eradicate the virus, leading to continued shedding and selection of mutants best able to survive. Similarly, at the population level, rising levels of infection and targeted vaccinations lead to promotion of mutants with different protein configurations that can escape the immune response.
501Y.v2 & 501Y.v3 both emerged in countries with high levels of prior infection, and appear to be better at infecting those already infected. All three variants bind more strongly to human ACE2 receptors, particularly when E484K is present.
Figure 1.2 - Convergent evolution of SARS-CoV-2 variants (ACE2 receptor above in light blue)
Observations on convergent evolution by Martin et al. chart a path towards a hypothetical "super variant" with mutations in up to 40 locations or "codons", with each stage posing greater challenges through better transmission, worse virulence and increased ability to escape the immune system. The battle is far from over.