  Currently, due to the COVID-19 pandemic the public life in most European
countries stopped almost completely due to measures against the spread of the
virus. Efforts to limit the number of new infections are threatened by the
advent of new variants of the SARS-COV-2 virus, most prominent the B.1.1.7
strain with higher infectivity. In this article we consider a basic two-strain
SIR model to explain the spread of those variants in Germany on small time
scales. For a linearized version of the model we calculate relevant variables
like the time of minimal infections or the dynamics of the share of variants
analytically. These analytical approximations and numerical simulations are in
a good agreement to data reported by the Robert Koch Institute (RKI) in
Germany.
