Table 1. Model parameters and initial values for variables.

Model parameter	Symbol	Value
Basic reproduction number	R0	1.6 [38, 39]
Transmission coefficient	β day−1	R0 × γ
Recovery rate	γ day−1	1/5 [40]
Rate of loss of cross-immunity	σ day−1	1/365 − 1/60 [20]
Vaccine efficacy	VE	0.5
Fraction vaccinated	f	0 − 1
Model variable	Symbol	Initial condition
Susc. to both strains	SS	1 − IS − VE f
Inf. with strain 1, susc. to strain 2	IS	2 10−4
Susc. to strain 1, inf. with strain 2	SI	2 10−4 @ t = ΔT
Time of introduction of strain 2	ΔT day	0 < ΔT < 100
Rec. from str. 1, cross-imm. to str. 2	RC	0
Rec. from str. 2, cross-imm. to str. 1	CR	0
Rec. from str. 1, susc. to str. 2	RS	0
Susc. to str. 1, rec. from str. 2	SR	0
Inf. with str. 1, rec. from str. 2	IR	0
Rec. from str. 1, inf. with str. 2	RI	0
Rec. from both strains	RR	0

The parameters for the simulations are indicated above unless otherwise specified in the figure legend.