Impact in children under the age of one of Tdap vaccination programme on pregnant women in Castelló

Introduction: The objective was to compare incidence rates of pertussis in children under the age of one in Castelló, before and after the introduction of vaccination of pregnant women in January 2015.

Methods: The incidence of the post-vaccine period (2015-2018) was compared with the pre-vaccine period (2011-2014) in all ages, in children from 3 to 11 months and under 3 months. The relative risks and their 95% confidence intervals (95% CI) were calculated.

Results: The overall rate of pertussis in all ages was higher in the post-vaccine period than in the pre-vaccine period (0.23 vs. 0.15 per 1.000 person-years), but decreased in those under 3 months. The relative risks were: 1.56 (95% CI 1.34-1.82) in all ages; 1.73 (95% CI 0.87-3.57) for children aged 3 to 11 months, and 0.35 (95% CI 0.16-0.69) for children under 3 months. A similar pattern was observed for hospitalised children.

Conclusions: The incidence rate in children under 3 months was reduced by 65% in the period after the intervention, and the hospitalisation risk rate by 71%, suggesting that the measure has been effective and specific for this age group.