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Background: Assessment of the kinetics of SARS-CoV-2 antibodies is essential in predicting risk of reinfection and durability of vaccine protection. Methods: This is a prospective, monocentric, longitudinal, cohort clinical study. Healthcare workers (HCW) from Strasbourg University Hospital were enrolled between April 6th and May 7th, 2020 and followed up to 422 days. Serial serum samples were tested for antibodies against the Receptor Binding Domain (RBD) of the spike protein and nucleocapsid protein (N) to characterize the kinetics of SARS-CoV-2 antibodies and the incidence of reinfection. Live-neutralization assays were performed for a subset of samples before and after vaccination to analyze sensitivity to SARS-CoV-2 variants. Findings: A total of 4290 samples from 393 convalescent COVID-19 and 916 COVID-19 negative individuals were analyzed. In convalescent individuals, SARS-CoV-2 antibodies followed a triphasic kinetic model with half-lives at month (M) 11À13 of 283 days (95% CI 231À349) for anti-N and 725 days (95% CI 623À921) for anti-RBD IgG, which stabilized at a median of 1.54 log BAU/mL (95% CI 1.42À1.67). The incidence of SARS-CoV-2 infections was 12.22 and 0.40 per 100 person-years in COVID-19-negative and COVID-19-positive HCW, respectively, indicating a relative reduction in the incidence of SARS-CoV-2 reinfection of 96.7%. Live-virus neutralization assay revealed that after one year, variants D614G and B.1.1.7, but less so B.1.351, were sensitive to anti-RBD antibodies at 1.4 log BAU/mL, while IgG 2.0 log BAU/mL strongly neutralized all three variants. These latter anti-RBD IgG titers were reached by all vaccinated HCW regardless of pre-vaccination IgG levels and type of vaccine. Interpretation: Our study demonstrates a long-term persistence of anti-RBD antibodies that may reduce risk of reinfection. By significantly increasing cross-neutralizing antibody titers, a single-dose vaccination strengthens protection against variants.

This protocol describes procedures for the detection of SARS-CoV-2 for two RdRp targets (IP2 and IP4). Based on the first sequences of SARS-CoV-2 made available on the GISAID database on January 11, 2020, primers and probes (nCoV_IP2 and nCoV_IP4) were designed to target the RdRp gene spanning nt 12621-12727 and 14010-14116 (positions according SARS-CoV, NC_004718).

Background The serologic response of individuals with mild forms of SARS-CoV-2 infection is poorly characterized. Methods Hospital staff who had recovered from mild forms of PCR-confirmed SARS-CoV-2 infection were tested for anti-SARS-CoV-2 antibodies using two assays: a rapid immunodiagnostic test (99.4% specificity) and the S-Flow assay (~99% specificity). The neutralizing activity of the sera was tested with a pseudovirus-based assay. Findings Of 162 hospital staff who participated in the investigation, 160 reported SARS-CoV-2 infection that had not required hospital admission and were included in these analyses. The median time from symptom onset to blood sample collection was 24 days (IQR: 21–28, range 13–39). The rapid immunodiagnostic test detected antibodies in 153 (95.6%) of the samples and the S-Flow assay in 159 (99.4%), failing to detect antibodies in one sample collected 18 days after symptom onset (the rapid test did not detect antibodies in that patient). Neutralizing antibodies (NAbs) were detected in 79%, 92% and 98% of samples collected 13–20, 21–27 and 28–41 days after symptom onset, respectively ( P = 0.02). Interpretation Antibodies against SARS-CoV-2 were detected in virtually all hospital staff sampled from 13 days after the onset of COVID-19 symptoms. This finding supports the use of serologic testing for the diagnosis of individuals who have recovered from SARS-CoV-2 infection. The neutralizing activity of the antibodies increased overtime. Future studies will help assess the persistence of the humoral response and its associated neutralization capacity in recovered patients. Fundings The funders had no role in study design, data collection, interpretation, or the decision to submit the work for publication.

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BK virus-associated nephropathy (BKVAN) causes renal allograft dysfunction. The current management of BKVAN relies on pre-emptive adaptation of immunosuppression according to viral load monitoring. However, this empiric strategy is not always successful. Therefore, pretransplant predictive markers are needed. In a prospective longitudinal study, we enrolled 168 kidney transplant recipients and 69 matched donors. To assess the value of BKV genotype-specific neutralizing antibody (NAb) titers as a predictive marker for BKV replication, we measured BKV DNA load and NAb titers at transplant and followed patients for 24 months. After transplant, 52 (31%) patients displayed BKV replication: 24 (46%) patients were viruric and 28 (54%) patients were viremic, including 13 with biopsy-confirmed BKVAN. At any time, patients with high NAb titers against the replicating strain had a lower risk of developing BKV viremia (hazard ratio [HR], 0.44; 95% confidence interval [95% CI], 0.26 to 0.73; =0.002). Each log increase in NAb titer decreased the risk of developing viremia by 56%. Replicating strains were consistent with donor transmission in 95% of cases of early BKV replication. Genotype mismatch between recipients' neutralization profiles before transplant and their subsequently replicating strain significantly increased the risk of developing viremia (HR, 2.27; 95% CI, 1.06 to 4.88; =0.04). A NAb titer against the donor's strain<4 log before transplant significantly associated with BKV replication after transplant (HR, 1.88; 95% CI, 1.06 to 3.45; =0.03). BKV genotype-specific NAb titers may be a meaningful predictive marker that allows patient stratification by BKV disease risk before and after transplant.

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has spread widely, causing coronavirus disease 2019 (COVID‐19) and significant mortality. However, data on viral loads and antibody kinetics in immunocompromised populations are lacking. We aimed to determine nasopharyngeal and plasma viral loads via reverse transcription‐polymerase chain reaction and SARS‐CoV‐2 serology via enzyme‐linked immunosorbent assay and study their association with severe forms of COVID‐19 and death in kidney transplant recipients. In this study, we examined hospitalized kidney transplant recipients with nonsevere (n = 21) and severe (n = 19) COVID‐19. SARS‐CoV‐2 nasopharyngeal and plasma viral load and serological response were evaluated based on outcomes and disease severity. Ten recipients (25%) displayed persistent viral shedding 30 days after symptom onset. The SARS‐CoV‐2 viral load of the upper respiratory tract was not associated with severe COVID‐19, whereas the plasma viral load was associated with COVID‐19 severity (P = .010) and mortality (P = .010). All patients harbored antibodies during the second week after symptom onset that persisted for 2 months. We conclude that plasma viral load is associated with COVID‐19 morbidity and mortality, whereas nasopharyngeal viral load is not. SARS‐CoV‐2 shedding is prolonged in kidney transplant recipients and the humoral response to SARS‐CoV‐2 does not show significant impairment in this series of transplant recipients.

We measured Anti-Spike (S), Nucleoprotein (N) and neutralizing antibodies (NAbs) in sera from 308 RT-qPCR + healthcare workers with mild disease, collected at two time-points up to 6 months after symptom onset. At Month 1 (M1), anti-S and N antibody levels were higher in males &gt; 50 years or with a body mass index (BMI) &gt; 25. At M3-6, anti-S and anti-N antibodies were detected in 99% and 59% of individuals, respectively. Anti-S antibodies and NAbs declined faster in males than in females, independently of age and BMI, suggesting an association of sex with evolution of the humoral response.