1-year monitoring of antibody response after SARSCoV- 2 vaccination in healthcare workers

ABSTRACT

The global strategy to control coronavirus disease 2019 (COVID 19) was based on the availability of COVID-19 vaccines [1]. Measurement of post-vaccination neutralizing antibodies (Abs) titer, has been shown to be related to protection from SARS-CoV-2 infection [2]. This work aims to improve vaccination data through the evaluation of neutralizing antibodies in triple-dose individuals. To this end, we have conducted a surveillance program focusing at measuring the concentration of IgG Abs against the Receptor Binding Domain (RBD) and neutralizing Abs (NT) anti-SARS-CoV-2 that block the interaction between RBD and the surface receptor cellular angiotensin converting enzyme (ACE2), in the serum of individuals in the vaccination course. The study was conducted on workers from the University of Rome "Tor Vergata" (nTOT=169) who received the Vaxzevria/AstraZeneca vaccine (n=56) and on healthcare workers of the PTV University Hospital who received the Comirnaty/Pfizer-BioNTech vaccine (n=113). Initially for both vaccines two doses were administered Vaxzevria (12 weeks apart), Comirnaty (2 weeks apart). After the second dose, for the two vaccines has been registered an increase in Abs values both for RBD and NT Abs. As the second dose of the two vaccines has been given at very different time, Pfizer vaccine resulted to response with a higher Abs values earlier in time than Astrazeneca. Moreover, Abs values recorded for those who received Pfizer vaccine are higher up to an order of magnitude. After 6 months from the first dose, the average value Abs titer was 300 BAU/ml and 200 BAU/ml for Pfizer and Astrazeneca respectively. All patients received the Pfizer vaccine as third dose. This last dose gave rise again to an increase of the Abs levels, the average values obtained were 5300 BAU/ml and 3900 BAU/ml for Pfizer and Astrazeneca respectively. As concern NT Abs, we observed a similar pattern to RBD one. After 5 months from the third dose, almost one year from the first dose, antibodies level was over 1000 BAU/ml. Recent work provided Abs cut-off value of immunity against SARSCoV- 2 infection. Values reported range from 200 to 600 BAU/ml [3,4].From this perspective our data have shown a low risk of infection after 1 one year for subjects with a complete vaccine cycle.