Fig. 2

Overview of the duplicated two-strain model structure to account for vaccine type- and dose-specific immunity against infection and severe disease in combination with differential waning immunity over time. The grey boxes embody the transmission structure included in Fig. 1 while only the Susceptible and Recovered are shown here (with \(R_i\) representing \(R_a\) and \(R_b\)). More information on the waning states is included in Table 1