Transversal sero-epidemiological study of Bordetella pertussis in Tehran, Iran

OBJECTIVES: Pertussis remains endemic despite high vaccine coverage in infants and toddlers. Pertussis vaccines confer protection but immunity wanes overtime and boosters are needed in a lifetime. Iran, eligible for the Expanded Program on Immunization that includes the primary immunization, implemented two additional booster doses using a whole-cell vaccine (wPV) at 18 months-old and about 6 years-old. Duration of protection induced by the wPVs currently in use and their impact as pre-school booster are not well documented. This study aimed at assessing vaccination compliance and at estimating the duration of protection conferred by vaccination with wPV in children aged < 15 years in Tehran, Iran. METHODS: Detailed information on vaccination history and capillary blood samples were obtained from 1047 children aged 3–15 years who completed the 3 doses-primary pertussis immunization, in Tehran. Anti-pertussis toxin IgG levels were quantified by ELISA. RESULTS: Compliance was very high with 93.3% of children who received the three primary and 1(st) booster doses in a timely manner. Timeliness of the 2(nd) booster was lower (63.3%). Rate of seropositive samples continuously and significantly increased from 1–2 to 5–6 years after 1(st) booster attaining 30.4% of children exhibiting serological sign of recent contact with B. pertussis. Second booster dating back 1 or 2 years was associated with high antibody titers, which significantly decreased within 3 years from injection. Among children who received 2(nd) booster injection more than 2 years before serum analysis, seroprevalence of pertussis infection was 8.4% and seropositivity rate was higher from the 10 years-old group. CONCLUSION: Seropositivity in children aged 6–7 years with no 2(nd) booster supports the need for a vaccination at that age. Adolescent booster may also be considered.