The study finds “Importantly, we detected SARS-CoV-2−reactive CD4+
T cells in ~40-60% of
unexposed individuals, suggesting cross-reactive T cell recognition between circulating ‘common cold’
coronaviruses and SARS-CoV-2.” (see last sentence of Summary).
In plain English, this means that 40-60% of the population has an immune system which is able to attack a Covid-19 infection, even without any prior exposure or vaccination.
Hence, only the remaining 40-60 % even needed to build immunity (via exposure to the virus) after the Coronavirus escaped the bioweapons lab in Wuhan, China.
Since about half the population had an immune-system, ready for the virus by default from the beginning, and every person who didn’t, builds immunity once in contact with the virus, the majority of the population can be expected to already be immune to Covid at this point.