Table 4. Mortality rate ratios (MRRs) for the interaction term (vaccination status x age group) from the final multivariate Poisson regression model of sex, age group (three levels) and vaccination status for the owned dog population present in the demographic surveillance area, modelled separately for 2012 and 2013. (See Table 3 for coefficients and MRRs of main effects).

		MRR (95% CI)
		2012	2013
Vaccination status (reference category: unvaccinated)
Vaccinated	0–3 months	0.11 (0.05–0.21)	0.31 (0.11–0.69)
	4–11 months	0.51 (0.08–2.86)	0.56 (0.08–3.79)
	≥12 months	1.08 (0.21–5.35)	0.82 (0.12–5.34)
Age group (reference category: 0–3 months)
4–11 months	Vaccinated	0.85 (0.23–3.35)	0.94 (0.28–3.86)
	Unvaccinated	0.18 (0.12–0.25)	0.52 (0.38–0.70)
≥12 months	Vaccinated	1.17 (0.38–4.07)	0.66 (0.21–2.57)
	Unvaccinated	0.12 (0.08–0.16)	0.25 (0.19–0.33)