TGFB1 and COVID-19: However, even after the onset of fever and a proinflammatory state or cytokine storm in more severe COVID-19 cases (correlating with immune recognition of infection, typically week 2 post-infection), evidence of ongoing TGF-β activity persists–such as IgA antibody class switching, high TGF-β blood levels, Th17 pathway activation, and the onset of lung fibrosis (54, 80, 86, 97, 105, 143).