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