Introduction: A large amount of recent research has focused on the nature of immunity elicited by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, particularly its robustness and the duration of protection it offers. As a vaccine's efficacy relies on its ability to induce a protective immune response, these questions remain particularly pertinent. An improved understanding of the immunity offered by the antibodies developed against SARS-CoV-2 in recovered patients is critical for the development of diagnostic tests and vaccines.
Methods: Our study aimed at the longitudinal analysis of antibody presence, persistence and its trend over eight months in a group of 30 COVID-19 recovered patients who tested positive by real-time quantitative PCR for SARS-CoV-2 in the period 1-30 March 2020. The subjects were divided into two groups based on disease severity: mild (n=17 subjects) and moderately-severe (n=13 subjects). The MAGLUMI 2019-nCoV lgM/lgG chemiluminescent analytical system (CLIA) assay was used to analyze these antibody titres.
Results: IgG antibody persistency was demonstrated in 76.7 % of the subjects (23 out of 30) at eight months post-infection. For the moderately-severe group, the titre trends for both IgM and IgG changed in a statistically significant way throughout the time period with IgM below and IgG above the set cut-off.
Conclusions: The results of this study highlight an important point in terms of the association between humoral immune response and disease severity. Patients who have experienced a relatively severe infection might develop a stronger immune response that could persist for a longer period.
Keywords: COVID-19; SARS-CoV-2; antibody trend; coronavirus; immunity.