Evaluation of IgG antibody response to diphtheria toxin one month after tetanusdiphtheria vaccination among 7-years-old children in a mountainous district in the Northern region of Viet Nam in 2020

Abstract

Under the outbreak of diphtheria disease mostly among preschool and primary school children, following the recommendations of WHO, Vietnam has implemented a second booster dose of diphtheria vaccine since 2019 for children at 7 years old in some at-risk provinces. This study evaluated the IgG antibody response to diphtheria toxid in a group of 7-year-old children living in Tran Yen district, Yen Bai province, after receiving one dose of Tetanus-diphtheria (Td) vaccine with reduced diphtheria toxoid in 2020. The study involved community intervention, monitoring 98 7 yearold children who received the Td vaccine to compare the proportion of children with a full protective antibody level (antibody concentration ≥ 0.1IU/mL) before and one month after vaccination. The results showed that the proportion of children with a protective antibody level against diphtheria toxin increased from 35% to 95% one month after vaccination. The intervention coefficient was 171%. 80% of children achieved long-term protective antibody levels (≥ 1.0IU/mL). The Td vaccine helped children achieve full and long-term protective antibody levels, even in those without the complete primary vaccination series and those with only baseline or no protection levels. Vaccinating 7-year-old children in areas with limited vaccination coverage and no actual circulating diphtheria cases is effective and necessary to prevent disease outbreaks. The study’s results suggest the Ministry of Health should consider including the Td vaccine in the Expanded Immunization Program for regular vaccination for 7-year-old children instead of approving current annual plans.