Concentration of specific anti-RBD IgG antibodies (Percentage of subjects with seroconversion 4-fold to pre-vaccination). Measurement time: Day 0; 42 and 70.Moreover; in a subset of subjects’ samples with seroconversion; the outcome will measure at months 4; 8 and 12 after completing scheme vaccination.

Concentration of specific anti-RBD IgG antibodies (Percentage of subjects with seroconversion 4-fold to pre-vaccination). Measurement time: Day 0; 42 and 70.Moreover; in a subset of subjects’ samples with seroconversion; the outcome will measure at months 4; 8 and 12 after completing scheme vaccination.