We see the blood has fewer protections through blood-donor information (fewer and fewer antibodies present in blood-donors). We then see variants evolve that are explicitly avoiding immune responses (aka: Gamma and Delta). And finally, we see these variants reinfect huge swaths of the population in practice.
Its not really that unbelievable of a story. It lines up with the science going on all around the world. Immune response wanes through some indirect measurement, variants rise, reinfections happen.
It also is within-a-magnitude of vaccine-induced immunity. So even if you get your immunity from vaccines, its seemingly waning after 8 months (Pfizer). 6 months / 8 months... that's close enough that its practically the same when it comes to these early / less rigorous studies. It seems that's how long our bodies immune response works vs this virus.
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Why do you think the virus is resurging in USA? There already was a huge surge (the 2020 summer surge and 2020 winter surge). For there to be yet another 2021 July/August surge??
Well: July 2021 was over 6 months since the last surge (December 2020/January 2021). Our collective immunities wore off. People _are_ getting reinfected.