Trifonova, Iva, Kim Ngoc, Teodora Gladnishka, Vladislava Ivanova, Metodi Kunchev, Ventsislav Mutafchiyski, and Iva Christova. “SARS-COV-2 SEROSURVEY AMONG BULGARIAN HEALTHCARE WORKERS BEFORE AND AFTER VACCINATION”. PROBLEMS of Infectious and Parasitic Diseases 50, no. 3 (August 14, 2023): 24–28. Accessed May 19, 2024. https://pipd.ncipd.org/index.php/pipd/article/view/50-3-4-sars-cov-2-serosurvey.