Seroepidemiology and Carriage of Diphtheria in Epidemic-Prone Area and Implications for Vaccination Policy, Vietnam

In 2019, a community-based, cross-sectional carriage sur-vey and a seroprevalence survey of 1,216 persons 1-55 years of age were conducted in rural Vietnam to investi-gate the mechanism of diphtheria outbreaks. Seropreva-lence was further compared with that of an urban area that had no cases reported for the past decade. Carriage prevalence was 1.4%. The highest prevalence, 4.5%, was observed for children 1-5 years of age. Twenty-seven as-ymptomatic Coerynebacterium diphtheriae carriers were identified; 9 carriers had tox gene-bearing strains, and 3 had nontoxigenic tox gene-bearing strains. Child malnu-trition was associated with low levels of diphtheria toxoid IgG, which might have subsequently increased child car-riage prevalence. Different immunity patterns in the 2 pop-ulations suggested that the low immunity among children caused by low vaccination coverage increased transmis-sion, resulting in symptomatic infections at school-going age, when vaccine-induced immunity waned most. A school-entry booster dose and improved infant vaccina-tion coverage are recommended to control transmissions.

Automated summary

In 2019, a community-based investigation was conducted in rural Vietnam to study the mechanism of diphtheria outbreaks. The study found a carriage prevalence of 1.4% and identified 27 asymptomatic carriers, some of whom carried toxigenic strains. Child malnutrition was associated with low levels of diphtheria toxoid IgG, which might have increased child carriage prevalence. The study recommended a school-entry booster dose and improved infant vaccination coverage to control transmissions.