O. Kounchev, G. Boyadzhiev, G. Simeonov, M. Kunchev, and Z. Kuncheva, “Implementation of Hidden Infections in the SEIR Model Analysis of the Omicron Variant Spread in Bulgaria”, C. R. Acad. Bulg. Sci., vol. 76, no. 6, pp. 953–961, June 2023.