Eight Months of Serological Follow-Up of Anti-SARS-CoV-2 Antibodies in France: A Study among an Adult Population.

BACKGROUND: Uncertainties remain regarding the nature and durability of the humoral immune response to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). AIM: This study investigated immunoglobulin G response and neutralizing activity to evaluate the mean antibody concentrations and response duration induced by each vaccination regimen in a French adult population. METHODS: A study including blood sampling and questionnaires was carried out from November 2020 to July 2021 with three separate follow-up phases. Spike proteins and neutralizing antibodies were quantified using ELISA and a virus-neutralization test. RESULTS: Overall, 295 participants were included. Seroprevalences were 11.5% (n = 34), 10.5% (n = 31), and 68.1% (n = 201) in phases 1, 2, and 3, respectively. Importantly, 5.8% (n = 17) of participants lost their natural antibodies. Antibody response of participants with only a prior infection was 88.2 BAU/mL, significantly lower than those vaccinated, which was 1909.3 BAU/mL (p = 0.04). Moreover, the antibody response of vaccinated participants with a prior infection was higher (3593.8 BAU/mL) than those vaccinated without prior infection (3402.9 BAU/mL) (p = 0.78). Vaccinated participants with or without prior infection had a higher seroneutralization rate (91.0%) than those unvaccinated with prior infection (65.0%). CONCLUSION: These results demonstrated that single infection does not confer effective protection against SARS-CoV-2.

Epidemiology and Clinical Symptoms Related to Seasonal Coronavirus Identified in Patients with Acute Respiratory Infections Consulting in Primary Care over Six Influenza Seasons (2014-2020) in France.

There is currently debate about human coronavirus (HCoV) seasonality and pathogenicity, as epidemiological data are scarce. Here, we provide epidemiological and clinical features of HCoV patients with acute respiratory infection (ARI) examined in primary care general practice. We also describe HCoV seasonality over six influenza surveillance seasons (week 40 to 15 of each season) from the period 2014/2015 to 2019/2020 in Corsica (France). A sample of patients of all ages presenting for consultation for influenza-like illness (ILI) or ARI was included by physicians of the French Sentinelles Network during this period. Nasopharyngeal samples were tested for the presence of 21 respiratory pathogens by real-time RT-PCR. Among the 1389 ILI/ARI patients, 105 were positive for at least one HCoV (7.5%). On an annual basis, HCoVs circulated from week 48 (November) to weeks 14-15 (May) and peaked in week 6 (February). Overall, among the HCoV-positive patients detected in this study, HCoV-OC43 was the most commonly detected virus, followed by HCoV-NL63, HCoV-HKU1, and HCoV-229E. The HCoV detection rates varied significantly with age (p = 0.00005), with the age group 0-14 years accounting for 28.6% (n = 30) of HCoV-positive patients. Fever and malaise were less frequent in HCoV patients than in influenza patients, while sore throat, dyspnoea, rhinorrhoea, and conjunctivitis were more associated with HCoV positivity. In conclusion, this study demonstrates that HCoV subtypes appear in ARI/ILI patients seen in general practice, with characteristic outbreak patterns primarily in winter. This study also identified symptoms associated with HCoVs in patients with ARI/ILI. Further studies with representative samples should be conducted to provide additional insights into the epidemiology and clinical features of HCoVs.

A Cross-Sectional Study of Exposure Factors Associated with Seropositivity for SARS-CoV-2 Antibodies during the Second Epidemic Wave among a Sample of the University of Corsica (France).

This study aimed to estimate the seroprevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection within the staff and student populations of the University of Corsica (France) during the second wave of the epidemic. METHODS: A cross-sectional survey was conducted from 23 November 2020 to 31 January 2021. The participants underwent blood sampling using a fingerstick procedure and completed an anonymized questionnaire. Sera were tested for the presence of anti-SARS-CoV-2 IgG (ELISA-S) and, if positive, with an in-house virus neutralization test (VNT). RESULTS: A total of 418 persons were included in the study. The overall seroprevalence was 12.8% (95% confidence interval (CI), 9.8-16.6%). A total of 15 (31%) of the 49 individuals who had a positive ELISA-S also had a positive VNT. Seropositivity was associated with living at the city campus during the week and on weekends (OR = 3.74 [1.40-12.00]), using public transportation/carpooling (OR = 2.00 [1.01-4.02]), and being in contact with a person who tested positive for SARS-CoV-2 (OR = 2.32 [1.20-4.40]). The main symptoms associated with seropositivity were "having had an acute respiratory infection" (OR = 3.05 [1.43-6.43]) and "experiencing loss of smell" (OR = 16.4 [5.87-50.7]). CONCLUSION: These results could be useful for SARS-CoV-2 prevention and control on university campuses.

Impact of the Second Epidemic Wave of SARS-CoV-2: Increased Exposure of Young People.

We aimed to use serological surveillance based on serial cross-sectional sampling of residual sera obtained from clinical laboratories to compare the differences in age and sex profiles of infected persons in the first and second waves of SARS-CoV-2 in Corsica, France. Residual sera were obtained, including samples from individuals of all ages collected for routine screening or clinical management by clinical laboratories. All the sera collected were tested for the presence of anti-SARS-CoV-2 IgG using a kit for semi-quantitative detection of IgG antibodies against the S1 domain of the viral spike protein (ELISA-S). Samples that were borderline and positive in ELISA-S were tested with an in-house virus neutralization test. During the second-wave period, we collected between 6 November, 2020 and 12 February, 2021, 4,505 sera from patients aged 0-101 years (60.4% women). The overall weighted seroprevalence of residual sera collected during the second-wave period [8.04% (7.87-9.61)] was significantly higher than the overall weighted seroprevalence estimated at the end of the first wave between 16 April and 15 June, 2020 [5.46% (4.37-7.00)] (p-value = 0.00025). Ninety-eight (30.1%) of the 326 samples tested in the VNT assay had a positive neutralization antibody titer. Estimated seroprevalence increased significantly for men [odds ratio (OR) OR = 1.80 (1.30-2.54); p-value = 0.00026] and for people under 30 years of age [OR = 2.17 (1.46-3.28); p-value = 0.000032]. This increase was observed in young adults aged 20-29 years among whom antibody frequencies were around four-fold higher than those observed at the end of the first wave. In conclusion, our seroprevalence estimates, including the proportion of the participants who had produced neutralizing antibodies, indicate that in February, 2021 the population of Corsica was still far from being protected against SARS-Cov-2 by "herd immunity."

Seroprevalence of SARS-CoV-2 IgG Antibodies in Corsica (France), April and June 2020.

Our aim was to assess the seroprevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection after the lockdown in a sample of the Corsican population. Between 16 April and 15 June 2020, 2312 residual sera were collected from patients with a blood analysis conducted in one of the participating laboratories. Residual sera obtained from persons of all ages were tested for the presence of anti-SARS-CoV-2 Immunoglobulin G (IgG) using the EUROIMMUN enzyme immunoassay kit for semiquantitative detection of IgG antibodies against the S1 domain of viral spike protein (ELISA-S). Borderline and positive samples in ELISA-S were also tested with an in-house virus neutralization test (VNT). Prevalence values were adjusted for sex and age. A total of 1973 residual sera samples were included in the study. The overall seroprevalence based on ELISA-S was 5.27% (95% confidence interval (CI), 4.33-6.35) and 5.46% (4.51-6.57) after adjustment. Sex was not associated with IgG detection. However, significant differences were observed between age groups (p-value = 1 E-5). The highest values were observed among 10-19, 30-39, and 40-49 year-old age groups, ranging around 8-10%. The prevalence of neutralizing antibody titers ≥40 was 3% (2.28-3.84). In conclusion, the present study showed a low seroprevalence for COVID-19 in Corsica, a finding that is in accordance with values reported for other French regions in which the impact of the pandemic was low.