a, Mammalian cell derived spike protein was used to study isotype/subclass distribution of antibodies (n = 13 positive samples). Lines represent the geometric mean. b, Microneutralization assay (n = 12) performed with authentic SARS-CoV-2. Lines represent curves fitted using an inhibitor (log) versus response variable slope with four parameters function in Graphpad Prism. Experiments were performed once.