Seroprevalence of Corynebacterium diphtheriae among vaccinated population of Rawalpindi/Islamabad, Pakistan

Diphtheria is a communicable disease of global significance, and its outbreaks have to be reported to the world community under the International Health Regulations (IHR). A pilot seroepidemiological survey was conducted to assess immunity status of diphtheria among healthy individuals of Rawalpindi/Islamabad (Pakistan), who had been administered at least one dose of the vaccine against the disease, as part of childhood vaccination. The study group comprised of 128 healthy subjects, grouped according to the decade representing their age. Antidiphtheria IgG levels were measured by Enzyme Linked Immunosorbent Assay (ELISA) method. The studied sample showed 100% prevalence of diphtheria antitoxin, confirming prior vaccination; however 49.2% exhibited only minimal protection against diphtheria. Full protection was observed in a significantly higher (p=0.013) percentage of males (54.45%) as compared to female subjects (33.33%). Maximum level of serum antibodies were seen in 1-10 year age group (0.195+0.031 IU/mL), which was significantly higher than that recorded in the age group of 11-20 (p=0.024) and above 30 years (p=0.0064). The present results emphasize the need for periodical booster immunization in adolescents and adults, after primary childhood immunization.