Table 1.

Description of model terms

Term	Description
a	Index of Age group
t	Index of Year
$S_t^a$	Unobserved number of Susceptible at time t, in age group a
$I_t^a$	Unobserved number of Infected at time t, in age group a
C t	Observed number of Cases reported in year t
V a()	Specifies the fraction of each age class immunized through vaccination
e t	Effect of unspecified influences on attack rate
π t	Attack rate in year t
p r	Probability of reporting a case
β 0	Parameter in attack rate function
β 1	Parameter in attack rate function
${\sigma }_e^2$	Attack rate variation