IgA and IgG antibodies in SARS-CoV-2 vaccinated health workers by a homemade ELISA diagnostic test

Abstract The SARS-CoV-2 pandemic has accelerated vaccine development and testing, an important step in its eradication. Health workers were included among the first subjects to be vaccinated, therefore it was necessary to check their immunological status after the first and second dose of vaccine. Serum samples belonging to 24 health workers undergoing vaccination for SARS-CoV-2 (Pfizer-BioNTech) were analysed: for 2 of them it was also possible to obtain a serum sample prior to the first dose of vaccine (zero time); antibody dosing was performed in 18 out of 24 after the first and second vaccination dose; in the remaining 6 healthcare workers a serum sample was obtained only after the second dose. In each serum sample, IgA and IgG antibodies to "Spike Receptor Binding Domain" (RBD) and "Nucleocapsid" (N) proteins were searched by ELISA test. Except for the two subjects for whom it was possible to have a serum sample before vaccination, the others were collected on day 18 from the first dose of vaccine and on day 8 from the second dose. Serum samples collected after the first dose of vaccine showed reactivity to anti-RBD IgG in 11 out of 18 healthcare workers and to IgA in 2 subjects. After the second dose all 24 samples showed the presence of anti-S IgG, while 5 revealed a reactivity for anti-S IgA. Three samples showed reactivity towards anti-N IgG. The ELISA test has shown all its effectiveness in controlling post vaccine immunity and in discriminating natural immunity from vaccine induced immunity.