Pertussis and number of doses of vaccine administered: a case control study

Objective: estimate the likelihood of pertussis according to number of vaccine doses received and age. Methods: Case-control study using 2007-2011 SINAN data. "Cases" were considered to be confirmed reported pertussis cases. "Controls" were the discarded cases. Results: 5,389 cases and 10,689 controls were included. In those aged 7-12 months, cases were twice as likely [OR: 2.1 (95% CI: 1.3-3.4)] when only 1 instead of 3 doses had been administered. In 1-3 year-olds, likelihood was greater in those not having boosters (1 booster expected) [OR 1 dose: 2.4 (95% CI: 1.6-3.8); OR 2 doses: 3.6 (95% CI: 2.2-6.1); OR 3 doses: 1.6 (95% CI: 1.3-2.2); OR empty set dose: 2.8 (95% CI: 1.7-4.8)]. In 7-15 year-olds, cases were 60% more likely in those having had 1 booster instead of 2 [OR: 1.6 (95% CI: 1.2-2.3)]. Conclusion: incomplete immunization increases likelihood of contracting pertussis in all age groups studied, mainly 7-15 years.