Current immunoassays and detection of antibodies elicited by Omicron SARS-CoV-2 infection.

The present study aimed to determine whether current commercial immunoassays are adequate for detecting anti-Omicron antibodies. We analyzed the anti-SARS-CoV-2 antibody response of 23 unvaccinated individuals 1-2 months after an Omicron infection. All blood samples were tested with a live virus neutralization assay using a clinical Omicron BA.1 strain and four commercial SARS-CoV-2 immunoassays. We assessed three anti-Spike immunoassays (SARS-CoV-2 IgG II Quant [Abbott S], Wantaï anti-SARS-CoV-2 antibody ELISA [Wantaï], Elecsys Anti-SARS-CoV-2 S assay [Roche]) and one anti-Nucleocapsid immunoassay (Abbott SARS-CoV-2 IgG assay [Abbott N]). Omicron neutralizing antibodies were detected in all samples with the live virus neutralization assay. The detection rate of the Abbott S, Wantai, Roche, and Abbott N immunoassays were 65.2%, 69.6%, 86.9%, and 91.3%, respectively. The sensitivities of Abbott S and Wantai immunoassays were significantly lower than that of the live virus neutralization assay (p = 0.004, p = 0.009; Fisher's exact test). Antibody concentrations obtained with anti-S immunoassays were correlated with Omicron neutralizing antibody concentrations. These data provide clinical evidence of the loss of performance of some commercial immunoassays to detect antibodies elicited by Omicron infections. It highlights the need to optimize these assays by adapting antigens to the circulating SARS-CoV-2 strains.

Evaluation of Three Quantitative Anti-SARS-CoV-2 Antibody Immunoassays.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019 and caused a dramatic pandemic. Serological assays are used to check for immunization and assess herd immunity. We evaluated commercially available assays designed to quantify antibodies directed to the SARS-CoV-2 Spike (S) antigen, either total (Wantaï SARS-CoV-2 Ab ELISA) or IgG (SARS-CoV-2 IgG II Quant on Alinity, Abbott, and Liaison SARS-CoV-2 TrimericS IgG, Diasorin). The specificities of the Wantaï, Alinity, and Liaison assays were evaluated using 100 prepandemic sera and were 98, 99, and 97%, respectively. The sensitivities of all three were around 100% when tested on 35 samples taken 15 to 35 days postinfection. They were less sensitive for 150 sera from late infections (>180 days). Using the first WHO international standard (NIBSC), we showed that the Wantai results were concordant with the NIBSC values, while Liaison and Alinity showed a proportional bias of 1.3 and 7, respectively. The results of the 3 immunoassays were significantly globally pairwise correlated and for late infection sera (P < 0.001). They were correlated for recent infection sera measured with Alinity and Liaison (P < 0.001). However, the Wantai results of recent infections were not correlated with those from Alinity or Liaison. All the immunoassay results were significantly correlated with the neutralizing antibody titers obtained using a live virus neutralization assay with the B1.160 SARS-CoV-2 strain. These assays will be useful once the protective anti-SARS-CoV-2 antibody titer has been determined. IMPORTANCE Standardization and correlation with virus neutralization assays are critical points to compare the performance of serological assays designed to quantify anti-SARS-CoV-2 antibodies in order to identify their optimal use. We have evaluated three serological immunoassays based on the virus spike antigen that detect anti-SARS-CoV-2 antibodies: a microplate assay and two chemiluminescent assays performed with Alinity (Abbott) and Liaison (Diasorin) analysers. We used an in-house live virus neutralization assay and the first WHO international standard to assess the comparison. This study could be useful to determine guidelines on the use of serological results to manage vaccination and treatment with convalescent plasma or monoclonal antibodies.

Estimating the impact of public health strategies on the spread of SARS-CoV-2: Epidemiological modelling for Toulouse, France.

The spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the resulting disease COVID-19 has killed over 2 million people as of 22 January 2021. We have used a modified susceptible, infected, recovered epidemiological model to predict how the spread of the virus in France will vary depending on the public health strategies adopted, including anti-COVID-19 vaccination. Our prediction model indicates that the French authorities' adoption of a gradual release from lockdown could lead in March 2021 to a virus prevalence similar to that before lockdown. However, a massive vaccination campaign initiated in January 2021 and the continuation of public health measures over several months could curb the spread of virus and thus relieve the load on hospitals.

The real seroprevalence of SARS-CoV-2 in France and its consequences for virus dynamics.

The SARS-CoV-2 virus has spread world-wide since December 2019, killing more than 2.9 million of people. We have adapted a statistical model from the SIR epidemiological models to predict the spread of SARS-CoV-2 in France. Our model is based on several parameters and assumed a 4.2% seroprevalence in Occitania after the first lockdown. The recent use of serological tests to measure the effective seroprevalence of SARS-CoV-2 in the population of Occitania has led to a seroprevalence around 2.4%. This implies to review the parameters of our model to conclude at a lower than expected virus transmission rate, which may be due to infectivity varying with the patient's symptoms or to a constraint due to an uneven population geographical distribution.

High immunogenicity of a messenger RNA-based vaccine against SARS-CoV-2 in chronic dialysis patients.

BACKGROUND: Patients with chronic kidney disease, dialysis patients and kidney transplant patients are at high risk of developing severe coronavirus disease 2019 (COVID-19). Data regarding the immunogenicity of anti-severe acute respiratory syndrome coronavirus 2 messenger RNA (anti-SARS-CoV-2 mRNA) vaccines in dialysis patients were published recently. We assessed the immunogenicity of anti-SARS-CoV-2 mRNA vaccine in dialysis patients. PATIENTS AND METHODS: One hundred and nine patients on haemodialysis (n = 85) or peritoneal dialysis (n = 24) have received two injections of 30-µg doses of BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech) that were administered intramuscularly 28 days apart. Those who were still seronegative after the second dose were given a third dose 1 month later. Anti-SARS-CoV-2 antibodies were tested before and after vaccination. RESULTS: Ninety-one out of the 102 patients who had at least a 1-month follow-up after the second (n = 97) or the third (n = 5) vaccine doses had anti-SARS-CoV-2 antibodies. The seroconversion rate was 88.7% (86 out of 97 patients) among SARS-CoV-2 seronegative patients at the initiation of vaccination. Receiving immunosuppressive therapy was an independent predictive factor for non-response to vaccination. CONCLUSION: Due to high immunogenicity and safety of mRNA vaccines, we strongly recommend prioritizing a two-dose vaccination of dialysis patients. A third dose can be required in non-responders to two doses. When possible, patients waiting for a kidney transplantation should be offered the vaccine before transplantation.

Side effect of a 6 p.m curfew for preventing the spread of SARS-CoV-2: A modeling study from Toulouse, France.

The spread of SARS-CoV-2 and the resulting disease Covid-19 has killed over 2 million people as of January 22, 2021. We have designed a model and used it to quantify the effect of a 6 p.m curfew on the SARS-CoV-2 epidemic in Toulouse, France. The data show that this measure can lead to the opposite effect from that intended due to larger groups of people on the authorized hours.