Elecsys anti sars cov 2 s elecsys s kit

Immunogenicity was assessed by measuring the concentration of anti-receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 before the first vaccination and 1 month after the second vaccination using an Elecsys Anti-SARS-CoV-2 S (Elecsys-S) kit (Roche Diagnostics, Mannheim, Germany), an automated electrochemiluminescence immunoassay. The test was performed in accordance with the manufacturer’s instructions. The concentration of anti-RBD antibodies is presented in this report as the binding antibody units per milliliter (BAU/mL) following the World Health Organization international standard for anti-SARS-CoV-2 immunoglobulin titers [20 (link)]. The Elecsys-S units were converted to BAU as follows: Elecsys-S U = 0.972 × BAU [21 (link)].

CoronaVac was administered as a 0.5 mL dose intramuscularly injected into the deltoid muscle, with two doses 3 weeks apart (at day 0 and day 21). Reactogenicity was monitored for 30 min after vaccination for immediate events. Thereafter, reactogenicity follow-up was continued at home at days 1 and 7 after vaccination.
A 6 mL blood sample was collected to determine serum levels of the total antibodies against the receptor-binding domain (anti-RBD) of the SARS-CoV-2 spike protein at baseline (before the first vaccine dose), and then 4 weeks after the second dose. Anti-RBD concentrations were measured by an electrochemiluminescence immunoassay Elecsys Anti-SARSCoV-2 S (Elecsys-S) kit (Roche Diagnostics, Mannheim, Germany).
The range of measurement of anti-RBD antibodies was 0.4–2500 U/mL. The cut-off value for a positive result was >0.8 U/mL, referenced from the manufacturer. Recently, the WHO released an international standard for the measurement of SARS-CoV-2 immunoglobulin that corresponds to the body’s immune response after natural infection or vaccination as binding antibody units (BAU) [23 (link)]. Therefore, we used this equation (Elecsys-S U = 0.972 × BAU) to transform Elecsys-S data from U to BAU [24 (link)].