Before revision:  Non-homogeneities in the basic parameters are easily included by integration for arbitrary distributions  of incubation and removal times , recovering the classical SEIR model under the assumption of exponential distributions .
After revision:  Non-homogeneities in the basic parameters are easily included by integration for arbitrary distributions . We present a new formulation, focussing on the SEIR concept that allows to include general distributions of incubation and removal times , recovering the classical SEIR model under the assumption of exponential distributions .