"he contracted the coronavirus there"
That about says it all. No 'health care system', no "Covid-19".
Whatever illnesses/conditions comprise the CCP virus disease it's not just a "virus" (exosome?). Some other organisms such as bacteria seem to be involved. I think Mercola believes certain bacteria harbor the "coronavirus" so that is how infection can evade the immune system. Might explain why antibiotics and anti-parasitic drugs are useful for treatment and prevention.