A mathematical study of the omicron variant in a discrete-time Covid-19 model Mahmoud H. DarAssi, Sadeq Damrah and Yousef AbuHour Eur. Phys. J. Plus, 138 7 (2023) 601 Published online: 10 July 2023 DOI: 10.1140/epjp/s13360-023-04233-5