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Trends in prevalence (top) and mean and median days (bottom) of undervaccination with DTwP or DTaP by birth cohort. All trends were significant using the Cochran-Armitage trend test (p < 0.0001) and linear regression (p < 0.0001). Numbers were listed in Table S2. DTwP, diphtheria, tetanus and whole-cell pertussis vaccine; DTaP, diphtheria, tetanus, and acellular pertussis vaccine.
