Understanding the immune responses elicited by SARS-CoV-2 infection is critical in terms of protection against reinfection and, thus, for public health policy and vaccine development for COVID-19. In this study, using either live SARS-CoV-2 particles or retroviruses pseudotyped with the SARS-CoV-2 S viral surface protein (Spike), we studied the neutralizing antibody (nAb) response in serum samples from a cohort of 140 SARS-CoV-2 qPCR-confirmed infections, including patients with mild symptoms and also more severe forms, including those that required intensive care. We show that nAb titers correlated strongly with disease severity and with anti-spike IgG levels. Indeed, patients from intensive care units exhibited high nAb titers; conversely, patients with milder disease symptoms had heterogeneous nAb titers, and asymptomatic or exclusive outpatient-care patients had no or low nAbs. We found that nAb activity in SARS-CoV-2-infected patients displayed a relatively rapid decline after recovery compared to individuals infected with other coronaviruses. Moreover, we found an absence of cross-neutralization between endemic coronaviruses and SARS-CoV-2, indicating that previous infection by human coronaviruses may not generate protective nAbs against SARS-CoV-2. Finally, we found that the D614G mutation in the spike protein, which has recently been identified as the current major variant in Europe, does not allow neutralization escape. Altogether, our results contribute to our understanding of the immune correlates of SARS-CoV-2-induced disease, and rapid evaluation of the role of the humoral response in the pathogenesis of SARS-CoV-2 is warranted.

Understanding the immune responses elicited by SARS-CoV-2 infection is critical in terms of protection from re-infection and, thus, for public health policy and for vaccine development against the COVID-19. Here, using either live SARS-CoV-2 particles or retroviruses pseudotyped with the SARS-CoV-2 S viral surface protein (Spike), we studied the neutralizing antibody (nAb) response in serum specimens from a cohort of 140 SARS-CoV-2 qPCR-confirmed patients, including patient with mild symptoms but also more severe form including those that require intensive care. We show that nAb titers were strongly correlated with disease severity and with anti-Spike IgG levels. Indeed, patients from intensive care units exhibited high nAb titers, whereas patients with milder disease symptoms displayed heterogenous nAb titers and asymptomatic or exclusive outpatient care patients had no or poor nAb levels. We found that the nAb activity in SARS-CoV-2-infected patients displayed a relatively rapid decline after recovery, as compared to individuals infected with alternative coronaviruses. We show the absence of cross-neutralization between endemic coronaviruses and SARS-CoV-2, indicating that previous infection by human coronaviruses may not generate protective nAb against SARS-CoV-2 infection. Finally, we found that the D614G mutation in the Spike protein, which has recently been identified as the major variant now found in Europe, does not allow neutralization escape. Altogether, our results contribute to the understanding of the immune correlate of SARS-CoV-2 induced disease and claim for a rapid evaluation of the role of the humoral response in the pathogenesis of SARS-CoV-2.

Reliable immunoassays are essential to early predict and monitor vaccine efficacy against SARS-CoV-2. The performance of an Interferon Gamma Release Assay (IGRA, QuantiFERON® SARS-CoV-2), and a current anti-spike serological test, compared to a plaque reduction neutralization test (PRNT) taken as gold standard were compared. Eighty vaccinated individuals, whose 16% had a previous history of COVID-19, were included in a longitudinal prospective study and sampled before and two to four weeks after each dose of vaccine. In non-infected patients, 2 doses were required for obtaining both positive IGRA and PRNT assays, while serology was positive after one dose. Each dose of vaccine significantly increased the humoral and cellular response. By contrast, convalescent subjects needed a single dose of vaccine to be positive on all 3 tests. Both IGRA and current serology assay were found predictive of a positive titer of neutralizing antibodies that is correlated with vaccine protection. Patients over 65 or 80 years old had a significantly reduced response. The response tended to be better with the heterologous scheme (vs. homologous) and with the mRNA-1273 vaccine (vs. BNT162b2) in the homologous group, in patients under 55 and under 65 years old, respectively. Finally, decrease intensity or absence of IGRA response and to a less extent of anti-spike serology were also correlated to reinfection which has occurred during the follow up. In conclusion, both IGRA and current anti-spike serology assays could be used at defined thresholds to monitor the vaccine response against SARS-CoV-2 and to simply identify non-responding individuals after a complete vaccination scheme. Capsule summary Two available specific tests (IGRA and anti-spike antibodies) could early assess the vaccine-induced immunity against SARS-CoV-2 at the individual scale, to potentially adapt the vaccination scheme in non-responder patients. Supplementary Information The online version contains supplementary material available at 10.1007/s10875-022-01354-x.