How to \textit{correctly} fit an SIR model to data from an SEIR model? (Q6620164)

The authors consider extensions of SIR models, called SEIR models, in which incubation times are included; that is, the individuals can, next to being Susceptible, Infectious, and Removed, also being ``Exposed'', that is Infected without being Infectious. It is shown how SEIR models can be approximated by SIR models with time-dependent parameters, and the deterministic limits, which are systems of ODEs are derived in the large-population limit, by a functional law of large numbers. Also a parameter estimation is considered. These models, although more complicated, are closer to being realistic. The novelty of the paper is the formal derivation of the relation between SIR and SEIR models