COVID-19(31) SARS-CoV-2(16) basic reproduction number(10) mathematical(9) Epidemic(8) Health(8) Chickenpox(8) Spread(8) mathematical model(7) Transmission(6) Data fitting(6) reduction(6) Epidemiology(6) Analysis(6) reported(6) social distancing(5) mathematical model.(5) COVID-19 pandemic(5) immunization(5) Hepatitis B virus(4) compartmental modeling(4) Novel coronavirus(4) vaccination(4) Lyapunov functional(4) mathematical modeling(4) variants of concern.(4) global stability(4) outbreak(4) underlying conditions(3) analyzed(3)