COVID-19 convalescent plasma donors: impact of vaccination on antibody levels, breakthrough infections and reinfection rate.

La Raja, M.; Pacenti, M.; Grimaldi, I.; Boldrin, C.; Cattai, M.; Solimbergo, E.; Battisti, A.; Scomazzon, M.; Roman, A.; Lazzaro, A. R.; Vicari, S.; Terzariol, S.; De Silvestro, G.

From April 2020 through May 2021 in Padova Province 3395 COVID-19 recovered patients were recruited as potential convalescent plasma donors and tested for SARS-CoV-2 antibodies. Since January 2021 COVID-19 vaccination campaign began in Italy, the impact of vaccination on antibody levels and suspect vaccine breakthrough infections in these subjects were investigated. Post-vaccination anti-Sars-Cov-2 antibody level in 54 previously infected subjects had an exponential increase compared to pre-vaccination level regardless of the number of vaccine doses. However after 100 days from vaccination SARS-CoV-2 antibody level tends to decline. Post-vaccination primary infections were detected in 15 cases, with 3 possible breakthrough infections after a full vaccination course. In these cases, antibody response after infection was present but weaker than the one of subjects vaccinated after natural infection. A trend toward stronger antibody response was observed with increasing distance between natural infection and vaccination. Additionally, 2 cases of asymptomatic reinfections are also discussed.