SARS-CoV-2 spike IgG titres up to 137 days following Comirnaty mRNA COVID-19 vaccination, Israel, February to May 2021

Background: Data regarding the long-term protection afforded by vaccination for the SARS-CoV-2 infection are essential for allocation of scarce vaccination resources worldwide. Methods: We conducted a retrospective cohort study aimed at studying the kinetics of IgG antibodies against SARS-CoV-2 in COVID-19-naive patients fully vaccinated with two doses of Comirnaty mRNA COVID-19 vaccine. Geometric mean concentrations (GMCs) of antibody levels were reported. Linear models were used to assess antibody levels after full vaccination and their decline over time. Results: The study included 4,740 patients and 5,719 serological tests. Unadjusted GMCs peaked 28-41 days after the first dose at 10,174 AU/mL ( 95% CI: 9,211-11,237) and gradually decreased but remained well above the positivity cut-off. After adjusting for baseline characteristics and repeated measurements, the antibodies half-life time was 34.1 days (95% CI: 33.1-35.2), and females aged 16-39 years with no comorbidities had antibody levels of 20,613 AU/mL (95% CI: 18,52622,934) on day 28 post-first- dose. Antibody levels were lower among males (0.736 of the level measured in females; 95% CI: 0.672-0.806), people aged 40-59 (0.729; 95% CI: 0.649-0.818) and >= 60 years (0.452; 95% CI: 0.398-0.513), and patients having haematological (0.241; 95% CI: 0.190-0.306) or solid malignancies (0.757; 95% CI: 0.650-0.881), chronic kidney disease with glomerular filtration rate (GFR) >= 30 (0.434; 95% CI: 0.354- 0.532) or with GFR < 30 mL/min (0.176; 95% CI: 0.109-0.287), and immunosuppression (0.273; 95% CI: 0.235- 0.317). Body mass index, cardiovascular disease, congestive heart failure, chronic obstructive pulmonary disease, diabetes and inflammatory bowel diseases were not associated with antibody levels. Conclusions: Vaccination with two doses resulted in persistently high levels of antibodies (= cut- off of 50 AU/mL) up to 137 days post- first-dose. Risk factors for lower antibody levels were identified.