Denis Y Logunov1, Inna V Dolzhikova2, Dmitry V Shcheblyakov2. 1. Federal State Budget Institution "National Research Centre for Epidemiology and Microbiology named after Honorary Academician N F Gamaleya" of the Ministry of Health of the Russian Federation, Moscow 123098, Russia. Electronic address: ldenisy@gmail.com. 2. Federal State Budget Institution "National Research Centre for Epidemiology and Microbiology named after Honorary Academician N F Gamaleya" of the Ministry of Health of the Russian Federation, Moscow 123098, Russia.