Longitudinal Analysis and Comparison of Six Serological Assays up to Eight Months Post-COVID-19 Diagnosis

BACKGROUND There is much data available concerning the initiation of the immune response after SARS-CoV-2 infection, but long-term data are scarce. METHODS We thus longitudinally evaluated and compared the total and neutralizing immune response of 61 patients to SARS-CoV-2 infection up to eight months after diagnosis by RT-PCR using several commercial assays. RESULTS Among the 208 samples tested, the percentage of seropositivity was comparable between assays up to four months after diagnosis and then tended to be more heterogeneous between assays (p < 0.05). The percentage of patients with a neutralizing titer decreased from 82% before two months postdiagnosis to 57% after six months. This decrease appeared to be more marked for patients under 65 years old and those not requiring hospitalization. The percentage of serology reversion at 6 months was from 11% with the WANTAI total assay to over 39% with the ABBOTT IgG assay. The neutralizing antibody titers decreased in parallel with the decrease of total antibody titers, with important heterogeneity between assays. CONCLUSIONS In conclusion, serological tests show equivalent sensitivity in the first months after the diagnosis of SARS-CoV-2 infection, but their performance later, postinfection, must be considered when interpreting the results.