Challenges of Mathematically Modelling the dynamics of CoViD-19 and its differrent strains

Up to 350 words. No references allowed. Abstracts may be submitted at a later date.
The use of Mathematical Modelling in describing the dynamics of the spread of COVID-19 soon presented challenges and many difficulties due to many factors: not only the variations of the tranmissibility of the successive variants, but athe different vaccination programmes, crises in hospital (and ICU) facilities and funerary systems, different cultures and religions