Effectiveness of acellular pertussis vaccine in a routine immunization program: a multicenter, case-control study in Japan.

In 2008, the number of pertussis cases increased substantially among Japanese adolescents, despite high coverage with acellular pertussis vaccine (DTaP). This study examined the effectiveness of DTaP vaccine in the routine immunization program in Japan. Between April 2009 and October 2012, we conducted a multicenter, case-control study, and compared the history of DTaP vaccination between 55 newly diagnosed pertussis cases and 90 age- and sex-matched controls. DTaP vaccine history was obtained by a self-administered questionnaire completed by their parents or guardians. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) of vaccination for development of pertussis. DTaP vaccination of ≥1 dose revealed a significantly lower OR for pertussis (OR=0.20, 95%CI, 0.04-0.97), and the OR of complete vaccination (4 doses) was 0.22 (0.04-1.05). Even after limiting subjects to those whose vaccination status could be confirmed by the immunization records, the negative associations were observed. The decreasing ORs of 4-dose vaccinees remained, even among subjects who had received the fourth dose ≥9.2 years earlier (OR=0.11, 95%CI, 0.01-1.02). In conclusion, DTaP vaccination had a preventive effect for pertussis. Effectiveness was observed even 9 or more years after the final dose.