Seroprevalence of Pertussis in School-entry Age Children in Libya, A Cross-sectional Study

Objective: In Libya, no pertussis booster doses are administered to children after 18 months of age. In light of evidence of waning of vaccineinduced immunity to pertussis, this study aimed to evaluate the waning of immunity in vaccinated school-entry age children, as measured by susceptibility to infection at population level. For this purpose, IgG and IgA levels were measured as markers of recent (infection in the last 6 months) and non-recent infections (infection in the last 12 months). Material and Methods: This was a cross sectional study undertaken in Tripoli, in February 2015. Children of school-entry age (> 5 to <= 7 years) were recruited on convenience basis at vaccination centers. Sera were tested for antibodies to pertussis. Results: Samples from 791 children (421 males and 370 females, mean age 6.50 were tested). All of the participants had received 4 doses of Whole cell pertussis containing vaccine in the first 2 years of life. The prevalence of recent and non-recent pertussis infection were 4.8% and 2.5%, respectively. The proportion of children with undetectable level of IgG was 76.1. Conclusion: The findings of this study showed significant circulation of Bordotella pertussis among vaccinated children by school-entry age. The circulation of B. pertussis in this population may be an indirect sign of waned immunity, which is simply corroborated by the absence of detectable antibodies in 76.1% of the children.