Twelve-month anti-SARS-CoV-2 antibody kinetics in COVID-19 patients from Bejaia, Algeria

Abstract

The COVID-19 pandemic has highlighted the importance of understanding long-term humoral immunity after SARS-CoV-2 infection. This study evaluated the kinetics and persistence of anti-SARS-CoV-2 immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in hospitalized patients who recovered and identified factors associated with antibody responses. A total of 96 patients hospitalized with real-time polymerase chain reaction-confirmed COVID-19 between June and September 2020 were included. Sequential serum samples were collected up to 365 days after symptom onset. Anti-SARS-CoV-2 IgM and IgG antibodies targeting spike (S) and nucleocapsid (N) proteins were evaluated on days 28, 90, 180, and 365 using chemiluminescent immunoassay (MAGLUMI). Clinical, epidemiological, and radiological data were analyzed. All convalescent patients developed detectable IgG antibodies, and 92.7% were IgG seropositive. Antibody titers and seropositivity rates declined over time; however, IgG antibodies remained more stable and persisted throughout the 12-month follow-up, whereas IgM antibodies became undetectable in most cases. Nevertheless, 12.5% of patients still had detectable IgM antibodies one year after symptom onset, whereas IgG seropositivity remained above 70%. Higher IgG titers were significantly associated with age ≥ 50 years, severe COVID-19, and SARS-CoV-2 pneumonia. Patients vaccinated before the final follow-up demonstrated a strong booster response with significantly higher IgG levels than unvaccinated individuals. In conclusion, symptomatic COVID-19 induces a durable humoral immune response that persists for at least 12 months. Hybrid immunity resulting from natural infection combined with vaccination appears to provide the strongest protection against SARS-CoV-2.