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When using a case-control study design to examine vaccine effectiveness, both the selection of control subjects and the consideration of potential confounders must be the important issues to ensure accurate results. In this report, we described our experience from a case-control study conducted to evaluate the effectiveness of acellular pertussis vaccine combined with diphtheria-tetanus toxoids (DTaP vaccine). Newly diagnosed pertussis cases and age- and sex-matched friend-controls were enrolled, and the history of DTaP vaccination was compared between groups. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) of vaccination for development of pertussis. After adjustment for potential confounders, four doses of DTaP vaccination showed a lower OR for pediatrician-diagnosed pertussis (OR = 0.11, 95% CI, 0.01–0.99). In addition, the decreasing OR of four doses vaccination was more pronounced for laboratory-confirmed pertussis (OR = 0.07, 95%CI, 0.01–0.82). Besides, positive association with pertussis was observed in subjects with a history of steroid treatment (OR = 5.67) and those with a recent contact with a lasting cough (OR = 4.12). When using a case-control study to evaluate the effectiveness of vaccines, particularly those for uncommon infectious diseases such as pertussis, the use of friend-controls may be optimal due to the fact that they shared a similar experience for exposure to the pathogen as the cases. In addition, to assess vaccine effectiveness as accurately as possible, the effects of confounding should be adequately controlled with a matching or analysis technique. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background In Japan, the seven-valent pneumococcal conjugate vaccine (PCV7) was introduced in 2010. PCV13 has replaced PCV7 since November 2013. Methods The effectiveness of PCV7 in protecting against invasive pneumococcal disease (IPD) in children aged <5 years was evaluated in a nationwide active population-based surveillance of IPD in 2008–2013 in 10 prefectures in Japan. Results 1181 cases were identified; 711 pneumococcal strains were analyzed for serotyping and antimicrobial resistance. Compared with the baseline IPD incidence (25.0 per 100,000), a 98% decline in IPD caused by PCV7 serotypes was found after the introduction of PCV7. This was partially offset by an increased incidence of IPD caused by PCV13 minus PCV7 and non-PCV13 serotypes, resulting in a 57% decline in overall IPD incidence. Absolute increases in the incidence rates of IPD caused by PCV13 minus PCV7 and non-PCV13 serotypes were 2.1 and 2.8 per 100,000 during the study period, respectively. The proportion of meropenem-nonsusceptible strains, especially with serotypes 19A and 15A, increased significantly after PCV7 introduction. Conclusions Our data confirmed a 98% decline in IPD incidence caused by PCV7 serotypes in children aged <5 years and serotype replacement after PCV7 introduction. This shows the importance of continuing surveillance of serotypes responsible for IPD and their antimicrobial resistance in Japan. [ABSTRACT FROM AUTHOR]