ABSTRACT
Background: Healthcare workers (HCW) were heavily exposed to iterative viral loads during SARS-CoV- 2/ COVID-19 pandemic. Post-infectious serum neutralizing anti-S/ SARS-CoV- 2 IgG antibody concentrations (anti-S sIgG), albeit a controversial biomarker of antiviral immune response efficacy is actually the only available in routine clinical practice. Method(s): Sequential serum anti-S sIgG measurement (chemiluminescence immunoassay;cut-off: >=1AU/mL) at 3 time-points: T0 = 50.3 +/- 15.3 days after symptom onset (dSo), 16.8 +/- 12.0 days after quarantine end (dQe);T1 = 143.1 +/- 43.9 dSo, 109.4 +/- 43.0 dQe;T2 = 241.3 +/- 75.5 dSo, 208.6 +/- 75.6 dQe;disease severity was classified as asymptomatic (IS1), mild/moderate (IS2) and severe/very severe (IS3) levels. We've enrolled 177 out of 193 positive SARS-CoV- 2/ RT-PCR HCW (8.3% initial dropout), 76.2% female/mean age = 39.6 +/- 11.7 years (y), 23.8% male/mean age = 41.1 +/- 13y, between March and May 2020, out of 4200 HCW of a university hospital. Out of these 177, 93.8% worked in COVID-19 high-risk areas, 72.5% were nurses or assistants, 7.8% had asymptomatic infection and 6.7% suffered serious illness demanding inpatient care. Result(s): At T0, 73.5% HCW (144+ve/166) yielded over-cutoff anti-S sIgG (sIgGoc), mean (sIgGm) = 12.5 +/- 9.1 AU/mL, IS1 = 7.3%, IS2 = 84.9% and IS3 = 7.8%;at T1, sIgGoc = 48.2% (80+ve /166), sIgGm = 2.7 +/- 4.9 AU/mL, IS1 = 7.8%, IS2 = 86.2%, IS3 = 6.0%;at T2, sIgGoc = 25.4% (31+ve /122;late drop out:44), sIgGm = 1.3 +/- 2.8 AU/ mL, IS1 = 8.9%, IS2 = 81.3%, IS3 = 9.8%. So, a progressive decrease in mean serum neutralizing anti-S/ SARS-CoV- 2 IgG antibody concentrations was evident during the first six months after disease, in consonance with available data. Under cutoff concentrations were evident 6 weeks after infection in 26.5% of HCW, in 51.8% after 4 months and 74.6% after 6 months, approximately and even in over-cutoff measurements, values approached the threshold of positivity. Conclusion(s): These results suggest that post-infectious natural immunity against SARS-CoV- 2 is tendentially weak and fast waning, reinforcing the need to repeatedly boost recovered HCW. This measure, together with the collective protection measures and the use of adequate personal protective equipment, will maximize the protection for HCW and patients altogether.