PROS1 and COVID-19: Indeed, based on these premises, a major explanation of adverse effects following COVID-19 vaccination could well be that mRNA vaccines induce in selected individuals excessive production of S protein, for too long and/or in inappropriate tissues and organs, and this occurrence is at present unpredictable, since systemic biodistribution and disposition of the COVID-19 mRNA vaccine has so far never been considered an issue, and as a consequence it has never been studied as it would have actually deserved.