Primary immunization with a triple diphtheria-tetanus-whole cell pertussis vaccine in Iranian infants: an analysis of antibody response.

Universal vaccination of neonates and children against diphtheria, tetanus and pertussis has had a tremendous impact on the control of these infectious diseases worldwide. Immunization by the triple diphtheria, tetanus and whole cell pertussis vaccine (DTwP) has been applied in Iran for almost 50 years. Periodic assessment of immunogenicity of this vaccine is an important aspect of successful mass vaccination programs. The present study was performed to assess the antibody response against tetanus, diphtheria and pertussis in a group of Iranian infants vaccinated with a local DTwP vaccine. In this prospective study, 330 infants received primary vaccination at 2, 4 and 6 months of age with DTwP vaccine manufactured by Razi Institute of Iran. Blood samples were taken 2-4 weeks after the third dose to assess seroprotection and geometric mean titers ( GMT) of specific antibodies. Among the 283 infants who completed the vaccination course, 98.2% and 100% developed antibodies against diphtheria and tetanus, respectively. The GMT of antibodies to tetanus, diphtheria and pertussis, were 2.09 IU/ml, 2.08 IU/ml and 8.73 EU/ml, respectively. Comparison of the results obtained from this study with those from previous studies performed in other countries revealed a similar GMT and protection rates for diphtheria and tetanus components. In the absence of well-established serological criteria, judgment about protection rate against pertussis has not been possible. A prospective vaccination study using the local DTwP vaccine in parallel to a WHO approved standard vaccine, could enable assessment of immunogenicity of the pertussis component.