No abstract

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Healthcare workers are among the most at-risk groups to get infected by SARS-CoV-2 due to the exposure to disease sources in specific working environment. However, after experiencing four waves of epidemics, there was a certain proportion of healthcare workers who have ever been diagnosed to be infected with SARS-CoV-2, regardless of whether they have a history of contact with or an unknown history of contact with an unidentified source of infection. This research aimed to identify the characteristics of healthcare workers who have not diagnosed with SARS-CoV-2 or have never been infected by SARS-CoV-2. 79 staffs of Hanoi Medical University were selected at the time of April 2022. 16 out of 79 individuals were infected with SARS-CoV-2 but had not been identified. 50% of this group were physicians working at primary care unit. Subjects who had been infected by SARS-CoV-2 showed greater levels of anti-receptor-binding domain (RBD) of SARS-CoV-2 antibodies than those who had never been infected (p=0.001). Anti-RBD antibody levels in 93.67% of research individuals were above the FDA-recommended threshold of 4.8 U/mL for the use of convalescent plasma. In the group that had never been infected by SARS-CoV-2, the antibody levels against RBD-SARS-CoV-2 were lower in those vaccinated above 90 days than those vaccinated below 90 days (p=0.02). 20.25% of research subjects who had never been diagnosed had infected by SARS-CoV-2, with greater levels of anti-RBD-SARS-CoV-2 antibodies than the uninfected group. In the uninfected group, antibody levels gradually decreased over time.