The new symptoms were principally dysosmia and transient headache, developing a median of 3.5 [2C4] months after the COVID-19 episode. The median time between the onset of symptoms and positive RT-PCR results was 2 [1C3] days, and the median time from onset of symptoms to blood sampling was 17 [14C23.25] days for the D21 time point, 59 [57C61] days for M2, and 97 [91C100] for M3. IgG, IgA, and IgM profile At the first time point (D21), all HCW had detectable IgG antibodies against SARS-CoV-2 N protein, IgA antibodies against SARS-CoV-2 receptor-binding domain (RBD), and IgA antibodies against SARS-CoV-2 spike protein (S). (%)?1 week8 (30.8)?2 weeks7 (26.9)?3 weeks6 (23.1)?4 weeks3 (11.5)?>1 month2 (7.7)New symptoms after a period of recovery, (%)?Yes5 (19.2)?No21 (80.8) Open in a separate windowpane The underlying detailed info is provided additionally within the source data file. All the HCW experienced symptoms consistent with COVID-19 (Table?1). The median duration of symptoms was 2 [1C3] weeks and 5 (19.2%) HCW developed new symptoms after a period of recovery. The new symptoms were principally dysosmia and transient headache, developing a median of 3.5 [2C4] months after the COVID-19 episode. The median time between the onset of symptoms and positive RT-PCR results was 2 [1C3] days, and the median time from onset of symptoms to blood sampling was 17 [14C23.25] days for the D21 time point, 59 [57C61] days for M2, and 97 [91C100] for M3. IgG, IgA, and IgM profile At the first time point (D21), all HCW experienced detectable IgG antibodies against SARS-CoV-2 N protein, IgA antibodies against SARS-CoV-2 receptor-binding website (RBD), and IgA antibodies against SARS-CoV-2 spike protein (S). In addition, 92.3% (24/26) had detectable anti-RBD IgG antibodies and 80.8% (21/26) had detectable anti-S IgG antibodies. Only 42.3% (11/26) had detectable anti-N/anti-S IgM BFLS antibodies. At M2, all HCW remained positive for anti-N IgG antibodies. The rates of seropositivity for anti-S IgG, anti-RBD IgG, and anti-N/anti-S IgM antibodies were 94.1% (16/17), 100% (17/17), and 64.7% (11/17), respectively. In the mean time, the anti-S IgA ML264 seropositivity rate declined to 88.2% (15/17) and that for anti-RBD IgA fell to 47% (8/17). At M3, the seropositivity rate for anti-N IgG experienced decreased slightly, to 96.2% (25/26). The proportion of anti-S IgG antibodies was 96.2% (25/26), and the proportion of anti-S IgA antibodies continue to decline, reaching 80.8% by this time point (21/26). In parallel, the seropositivity rate for anti-RBD IgG antibodies declined to 92.3% (24/26) and that for anti-RBD IgA fell to 38.5% (10/26). We were able to detect anti-N/anti-S IgM antibodies in ML264 15/26 ML264 HCW (57.7%). We then compared the changes in the levels of these antibodies over time, to assess the intensity of the immune response to SARS-CoV-2 (Fig.?1). Anti-S and anti-RBD IgA antibody levels decreased significantly between D21 and M2 (ideals were identified in two-sided Wilcoxon signed-rank checks. Resource data are provided as a Resource Data file. Changes in Nab titers over time We ML264 analyzed the neutralizing activity of serum samples from your 26 HCW inside a disease neutralization test (VNT). At D21, all sera (100%) harbored NAbs having a neutralizing titer 1:5, the median neutralizing titer becoming 1:20 [1:10C1:40] (Fig.?2). At M2, serum samples from 88.2% (15/17) of the HCW were still neutralizing, having a median neutralizing titer of 1 1:20 [1:5C1:20]. By M3, serum samples from another two HCW experienced lost their neutralizing activity; serum samples from 84.6% (22/26) of the HCW remained neutralizing, having a median titer of 1 1:10 [1:5C1:20]. NAb titers decreased significantly between D21 and M2 (ideals were identified in two-sided Wilcoxon signed-rank checks. Resource data are provided as a Resource Data file. We also tested the same 10 HCoV serum samples (2 HCoV-HKU1, 3 HCoV-OC43, 3 HCoV-NL63, and 2 HCoV-229E) to assess cross-neutralization capacities between HCoV and SARS-CoV-2. None of these serum samples.