Higher values of CRP, ESR, IL-6, and β-2-glycoprotein antibodies as well as higher frequencies of CRP elevation and any Ig decrease were observed for post-COVID-19 patients compared to healthy controls (p = 0.009; p = 0.007; p = 0.004; p = 0.031; p = 0.007; p = 0.015, respectively). Here, CRP is linked to COVID-19.