Determination of SARS-CoV-2 antibody levels
Serum was separated from clot and blood cells by centrifugation (1000 xg , 10 min) using gel separator tubes. Samples were either directly tested for SARS-CoV-2 anti-nucleocapsid-IgG antibodies by the Architect i2000 analyzer on the day of sample collection or were separated into a secondary tube and frozen at -200C until the test was performed. After performing the test, samples were frozen at -200C. For determination of SARS-CoV-2 anti-spike (S1/S2) IgG and IgM antibody titers, samples were thawed and mixed by vortex, and then subjected to ready-to-use assays on automated analyzers, as detailed in Table 1.