Impact of vaccine delays at the 2, 4, 6 and 12 month visits on incomplete vaccination status by 24 months of age in Quebec, Canada

Table 3 Proportion of incomplete vaccination status by 24 months of age attributable to new vaccine delays, 2006–2016 (N = 3508)^a

Vaccination visits	Incomplete vaccination status		Risk difference for incomplete vaccination status		Relative risk of incomplete vaccination status	% of cases exposed	Attributable risk in the population
Vaccination visits	With a new vaccine delay % (n/N)	Without a vaccine delay % (n/N)	Unadjusted	Adjusted^b (95% CI)	Adjusted^b (95% CI)		Adjusted (95% CI)^c
DTaP at 2 months	46.4% (96/207)	11.1% (361/3250)	35.3%	27.7% (22.2%; 28.2%)	3.6 (2.95; 4.37)	21.0%	16.1% (8.4%; 23.7%)
DTaP at 4 months	24.3% (64/263)	9.8% (292/2982)	14.5%	13.8% (13.4%; 14.0%)	2.5 (1.91; 3.18)	18.0%	10.6% (1.4%; 19.3%)
DTaP at 6 months	19.6% (71/362)	8.3% (217/2616)	11.3%	10.5% (10.3%; 10.8%)	2.3 (1.81; 3.02)	24.7%	14% (3.9%; 23.5%)
Measles at 12 months	17.5% (99/567)	4.6% (94/2025)	12.8%	8.8% (8.5%; 9.0%)	2.9 (2.12; 3.85)	51.3%	31.8% (20.5%; 40.1%)

CI Confidence interval estimated using bootstrap with 1000 replications
^aAnalysis restricted to the 2-year cohort and to children born in Quebec. Unvaccinated children: 51 at 2 months, 5 at 4 months, 4 at 6 months and 24 at 12 months
^bRisk difference estimated with standardization using predicted probabilities calculated from Robust Poisson multivariable regression. Incomplete vaccination for common antigens only (ie. DTaP-VPI-Hib. MMR and Men-C-C vaccines). Risk difference and relative risk adjusted for survey year, mother’s age at child birth, sex, mother’s education, child’s rank, daycare attendance, child’s health condition, gestational age, family type, main vaccine provider, missed opportunities. Analysis restricted to children with no vaccine delays at previous dose. Mother’s language, mother’s country of origin and the birth attendant were excluded from this analysis as they were not collected in 2006 and 2008 (more than 10% of missing)
^cSimilar results were observed using the following formula: \( \mathrm{ARp}=\frac{\mathrm{PCE}\ast \left(\mathrm{RR}-1\right)}{\mathrm{RR}} \) PCE = proportion of cases exposed (i.e. proportion of children with incomplete vaccination status with new vaccine delays)

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