Incidence of Tozinameran Adverse Events among the Employees of National Cancer Institute.

e18724 Background: Active immunization seems to be the most effective protection against COVID-19. The objective of this prospective study was to explore the side effects of mRNA vaccine Tozinameran and possible differences in their incidence between different categories of employees at the National Cancer Institute in Bratislava, Slovakia (NCI). Methods: Four hundred and thirteen subjects (89 men) were enrolled into this ongoing prospective study in January, 2021. Median age was 47 years (range 19-79 years). Majority were healthcare professionals (N=306), including nurses (N=125), medical-technical workers (N=89), and physicians (N=42). Presence of side effects was entered by the physicians into electronic data files and their accuracy validated for each subject by an independent investigator. Number of adverse events in the subgroups were compared with log-rank test. Results: At median follow up of 4 weeks, injection site pain (63.0%), pain in the extremity (45.5%), and fatigue (28,6%) belonged among the most common adverse events of Tozinameran. Median number of side effects was 2 (range 0-13). Adverse event incidence was significantly higher in females compare to males (median number 2 vs. 1, P < 0.00001). In a subgroup of healthcare professionals, we found a significantly higher incidence of side effects compared to non-healthcare workers (median number 2 vs. 1, P = 0.00017). Conclusions: In this study, incidence of Tozinameran adverse events was significantly higher in females vs. males and healthcare professionals vs. non-healthcare workers. All side effects were mild and no new safety signals were recognized during follow-up. Key Words: Tozinameran, Active Immunization. COVID-19. Healthcare Professionals. Adverse Events. This study was supported by National Cancer Institute in Bratislava (SK) and OncoReSearch (SK).