However, despite all these limitations, what the modelling indicates is that the normal stability of the AP in health might, after certain forms of activation and for periods of days or even weeks, be ‘capsized’ in a transient stability with low or very low C3 circulating levels and high FB levels pending the clearance of the large excesses of circulating FB that can be generated in COVID-19 [42]. Here, C3 is linked to COVID-19.