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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]

Abstract: The incidence of reported cases with pertussis has increased in young adults in Japan and the lack of additional booster immunizations containing pertussis components is suspected to be one of the causal reasons. Instead of DT immunization at 11–12 years of age, safety and immunogenicity were investigated using 0.2ml and 0.5ml of DTaP. 176 subjects in DTaP 0.5ml, 178 in DTaP 0.2ml, and 197 in DT 0.1ml groups were enrolled in clinical trial. The relative risk of local reactions in the DTaP 0.2ml group compared to the DT 0.1ml group was 1.13 (95% CI: 0.97–1.30), and that of the DTaP 0.5ml to the DT 0.1ml group was 1.34 (95% CI: 1.18–1.53). The relative risks of local pain and heat were 1.62 (95% CI: 1.33–1.98) and 1.59 (95% CI: 1.19–2.13), respectively, in the DTaP 0.5ml group compared to the DT 0.1ml group. Sero-positive rates against PT and FHA were 54% and 82% before immunization and increased to >95% for both after vaccination with no significant difference in GMT. Instead of the scheduled DT program, 0.2ml of DTaP was acceptable and demonstrated efficient immunogenicity. [ABSTRACT FROM AUTHOR]

• In Japan, Prenatal DTaP vaccination lacks required safety information. • Pertussis seroprevalence is approximately 70% among pregnant Japanese women. • Maternal antibody titers in early pregnancy reflect infant antibody titers. • Preconception DTaP vaccination is one way to obtain maternal immunity. • A national survey to evaluate the safety information of prenatal DTaP is necessary. An increasing number of countries have been introducing acellular pertussis vaccination during pregnancy for the prevention of neonatal pertussis. In response to the fact that infantile pertussis cases of 0–5 months age groups remained unchanged despite the universal vaccination program, prenatal pertussis vaccination has been a rising issue in Japan. Hence, we investigated the seroprevalence of pertussis, diphtheria, and tetanus antibodies in Japanese pregnant women and neonates, and evaluated the necessity of diphtheria-tetanus-acellular pertussis (DTaP) vaccination during the preconception or prenatal period. Maternal PT-IgG (EIA) and FHA-IgG (EIA) for the first trimester, within 1 week after delivery, and cord blood were collected, along with colostrum pertussis-IgA (ELISA), diphtheria-IgG (EIA), tetanus-IgG (EIA), and blood samples from the first trimester. The maternal seroprevalence of PT-IgG and FHA-IgG was 69 % and 75 %, respectively. All tested participants were positive for diphtheria-IgG and tetanus-IgG (100 %). First trimester PT-IgG/FHA-IgG antibody titers were significantly associated with cord blood PT-IgG/FHA-IgG titers (P < 0.001). We found that pertussis seroprevalence among pregnant Japanese women was approximately 70 %. The antibody seropositivity rate of pertussis was lower than that of diphtheria and tetanus. Fetal acquired passive immunity against pertussis is higher when the level of maternal antibody in the first trimester is sufficient. At least 30 % of study population did not reach to the threshold value to provide sufficient pertussis immunity for the neonates and themselves. The acellular pertussis vaccine (DTaP) approved in Japan lacks safety information for pregnancy, hence, a solution for prompt administration of prenatal acellular pertussis vaccination might be introducing DTaP in the preconception period. [ABSTRACT FROM AUTHOR]

There is some evidence that Bordetella pertussis (B. pertussis) can co-infect with viral respiratory infections in young infants. B. pertussis infection was studied by culture, polymerase chain reaction (PCR), and loop-mediated isothermal amplification (LAMP) from nasopharyngeal swabs (NPSs) in 49 infants < 12 months of age, who were admitted for lower respiratory tract infections during the winter season. Seven other possible viral pathogens were documented by antigen detection or PCR in NPSs. The clinical feature of infants with mixed infection of B. pertussis and respiratory viruses were examined. Overall, B. pertussis infection was found in 10 (20.4%) cases, nine were less than 6 months of age and seven were unvaccinated. Viral etiology was found in 41 (84%) cases and pertussis-viral co-infection was present in eight patients, five of whom had mixed infection with respiratory syncytial virus. Only the presence of staccato coughing, cyanosis, and lymphocytosis were significantly different in B. pertussis -positive cases compared with B. pertussis -negative cases. Of the 10 pertussis cases, only the culture-positive cases showed the typical symptoms and laboratory findings of pertussis in addition to virus-associated respiratory symptoms with severe hospital course, whereas cases identified as DNA-positive lacked the characteristics of pertussis and their clinical severities were the same as B. pertussis -negative cases. In the absence of typical paroxysmal cough and lymphocytosis, we should carefully consider diagnosis of pertussis in young children hospitalized for presumed viral respiratory illness according to local epidemiological surveillance. [ABSTRACT FROM AUTHOR]