[JamesBarney]

The link you specified specifically says that previous infection could be why Omicron appears less severe..

> “Epidemiological tracking shows a steep trajectory of new infections, indicating Omicron’s rapid spread, but so far with a flatter trajectory of hospital admissions, possibly indicating lower severity,” explains Dr Noach. “This lesser severity could, however, be confounded by the high seroprevalence levels of SARS CoV-2 antibodies in the general South African population, especially following an extensive Delta wave of infections.”