Study of Serologic Response Rate to Pertussis after Administration of the Third Dose of Pentavalent Vaccine in Children 12 Months Old in Karaj City, Iran

Background: After substitution of Pentavalent vaccine with diphtheria, tetanus, pertussis (DTP) in the Iranian National Vaccination program with 3 Pentavalent (three times vaccination with Pentavalent vaccine at months 2, 4, and 6) in 2014 and the lack of published research in the field of immunogenicity of pertussis component of this vaccine, the efficacy of pertussis vaccine was studied 6 months after the last dose of Pentavalent vaccine in Iranian infants.  Materials and Methods: Five hundred blood samples were collected from healthy one-year-old children who attended 18 health care centers of Karaj, Iran for routine vaccination selected by cluster sampling (2016). Sampling checklists contained demographic information and risk factors. The blood samples were sent to the laboratory for determination of Immunoglobulin G (IgG) and IgA anti-pertussis antibody titer by ELISA method. Data were analyzed by STATA software (version 14.0). Results: 82.7% (n=413) of children (95% confidence interval [CI]: 79.49-86.11) had IgG titer less than 16 IU/ml against pertussis (no immune response), and 17.3% (n=87) had equal or greater than 16 IU/ml IgG titer against pertussis (95% CI: 13.89-20.51). IgA titer against pertussis was less than 8U/ml in all cases. Anti-pertussis IgG geometric mean titer (GMT) was 15.80 U/ml (95% CI: 15.26-16.36), and IgA GMT was 6.26 U/ml (95% CI: 6.22-6.30). There was not a significant correlation between titer of pertussis antibody and demographic factors. Conclusion: Based on low IgG titer in vaccinated children, immunogenicity of pentavalent vaccine in Iranian children needs more investigation. In this study, 100 % of children had negative serologic response (IgA