Seroprevalence of Diphtheria in Antananarivo, Madagascar, and Cambodia

This is the authors' abstract. We don't add key points for this paper.

Background: Amidst a global resurgence of diphtheria cases with numerous outbreaks recorded worldwide since 2000, a better understanding of this vaccine-preventable disease's circulation is needed. Methods: We retrospectively analyzed sera from 2 sero-epidemiological cross-sectional studies in Madagascar and Cambodia on fully primo-vaccinated 3- to 15-year-olds. Using enzyme-linked immunosorbent assay (ELISA) and seroneutralization (Vero Cell TNT) for the 3- to 8-year-olds with low ELISA titration values (<0.01 IU/mL), we assessed (i) the duration of protection by primary vaccination for 3- to 8-year-olds and (ii) the level of diphtheria in children and adolescents. Seropositivity was defined as a titration value (by ELISA or TNT) of at least 0.1 IU/mL and was used as a proxy for diphtheria infection among individuals >6 years postvaccination. Results: < .01) in Madagascar. In Cambodia and Madagascar, respectively, 27.8% and 20.7% of the participants whose primary vaccination was performed >6 years earlier were seropositive, suggesting diphtheria infection. In both countries, we observed a higher rate of infected children when the last vaccine injection had been received 7-8 years or 11-12 years earlier vs 5-6 years earlier. Conclusions: Our data show that the disease is present at high levels in Cambodia and Madagascar and that the national recommendation-primary vaccination-is not sufficient: Booster doses appear necessary at around 6 years of age and for adolescents, as recommended by the World Health Organization.