Vaccine - (Page 4) M. Oviedo et al. / Vaccine 26 (2008) 6157–6164 6159 Model BN3. Includes, in addition to the variables in model BN2, the interaction between year of report and vaccination (year × vac). log(cases) = ˇ0 + ˇ1 year + ˇ2 age01 + ˇ3 age02 + ˇ4 age03 + ˇ7 vac + ˇ8 year × vac + ˇ5 sin + ˇ6 cos 2t amplitude 2t amplitude (4) + log(population) + ε Yearly amplitudes for the model (range: 5–7 years) were considered. Model BN4. Includes, in addition to the variables in model BN0, the proportion of vaccination coverage (vac) and the interaction between year of report and vaccination (year × vac). log(cases) = ˇ0 + ˇ1 year + ˇ2 age01 + ˇ3 age02 + ˇ4 age03 + ˇ7 vac + ˇ8 year × vac + log(population) + ε 3.1. Sensitivity analysis Various sensitivity analyses were carried out. Firstly, the percentage of vaccination was varied, weighted as a function of the population for each year of age. The percentage of vaccination (vac) calculated for the 12–18 years age group was introduced in model BN5 (see Eq. (6)) as (vac* ): 11% in 1999, 23% in 2000, 36% in 2001, 49% in 2002, 63% in 2003, 77% in 2004 and 91% in 2005. Model BN5. The variable vaccination was used with vaccination coverages calculated as a function of the population of each age group and year. log(cases) = ˇ0 + ˇ1 year + ˇ2 age01 + ˇ3 age02 + ˇ4 age03 + ˇ7 vac∗ + ˇ8 year × vac∗ + ˇ5 sin + ˇ6 cos 2t amplitude 2t amplitude (6) (5) Two additional sets of information were introduced into model BN3, producing model BN6 (see Eq. (7)). Firstly, as risk groups were vaccinated from 1995 onwards, we estimated an annual increase in vaccination coverage of 1% from ≥18 years of age. Secondly, with respect to vaccination coverage of children <3 years of age, it was estimated that 6.33% [22] of children born in 2001 were vaccinated, representing a vaccination coverage of 1.58% of the total number of children aged <12 years in our study. Model BN6. The variable vaccination was used with additional information on the vaccination coverage of risk groups and vaccinated children (vac** ). log(cases) = ˇ0 + ˇ1 year + ˇ2 age01 + ˇ3 age02 + ˇ4 age03 + ˇ7 vac∗∗ + ˇ8 year × vac∗∗ + ˇ5 sin + ˇ6 cos 2t amplitude 2t amplitude (7) + log(population) + ε Finally, in order to calibrate the general robustness of the model BN4 over time, the estimated coefficients were re-estimated recursively, extracting the data from a whole year in each iteration. The iterative model B4 collects the range and mean of the estimated parameters by means of this procedure. 4. Results Fig. 1 shows the comparison between the reported hepatitis A incidence rate by age corresponding to the pre- and postvaccination periods. The lowest and most-homogenous incidence occurred in people aged ≥40 years (rate of 0.9 per 100,000 personyears for the 1992–1998 pre-vaccination period and 0.6 for the 1999–2005 period) whereas there was a heterogenous reduction in incidence for other age groups; in children <12 years, the incidence of reported cases was reduced by half (14.6 per 100,000 personyears for the 1992–1998 period and 7.6 for the 1999–2005 period). In the 12–18 years age group, the reduction was much greater (6.9 + log(population) + ε Fig. 1. Distribution of the reported incidence rate of hepatitis A in Catalonia before and after vaccination according to age.
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