Table 2.

Parameters in the transmission process

Parameter	Meaning	Value/Source
θ	Cross-immunity: reduction in the susceptibility to one strain following natural infection with another strain	90%; 70%; 50%
V	Vaccine valency	“Bivalent”; “Monovalent”
L	Vaccine coverage levels in the 5 age groups	40% children, 30% adults (baseline scenario); (37%,27%); (30%,22.7%); (24%,18%) (alternative)
ni	Population size, age group i. Age groups are (0–4,5–17,18–49,50–64,65+)	[28]
cij	Contact rate between age groups i and j	[26]
$s_i^k$	Susceptibility to strain k in age group i	Drawn uniformly between [0.75,1] for age groups 1–3; 0.65 for age group 4; 0.4 for age group 5
w()	Serial interval distribution	[29]
λ	Scaling parameter for transmission (eq. 1)	See description following eq. 1
D	Delay (in days) between the introduction of the first infected individuals for strain 2 vs. 1	Drawn uniformly between [−35,35]
E	Vaccine efficacies against the two strains for the monovalent and the bivalent vaccines	Vaccine-type strain: 40%/non-elderly, 30%/elderly. Non-vaccine strain: 40%/non-elderly, 30%/elderly (bivalent vaccine); Drawn uniformly between [0,20%]/non-elderly, [0,15%]/elderly (monovalent vaccine)