Tetanus Toxin Antibody Levels in Pre-School Nigerian Children after Three Doses of Diphtheria-Pertussis-Tetanus/Pentavalent Immunization: A Cross-Sectional Study

Background: Post-neonatal tetanus is an important problem. Prevention of tetanus in Nigeria is via immunization with three doses of Diphtheria-Pertussis-Tetanus (DPT)/Pentavalent vaccine at 6, 10 and 14 weeks. The anti-tetanus antibody levels of these children are not known after they had received DPT3/Pentavalent vaccines. Aim: This work was to determine the anti-tetanus antibody (IgG) response in Nigerian children aged six months to five years who had received three doses of DPT vaccine in early infancy. Methods: Children aged six months to five years who were attended to in the University of Calabar Teaching Hospital for acute illnesses were recruited. Their anti-tetanus IgG levels were measured using Enzyme Linked Immunosorbent Assay (ELISA). The optimal cut-off level of ≥0.1 IU/ml was used as the protective level. Data was analysed using the Statistical Package for Social Sciences (SPSS) version 20.0 with simple proportions and percentages. Students’ “t” test and ANOVA were used to compare quantitative variables while Chi-square and Fisher’s exact test were used to compare categorical data. Results: Four hundred and eighteen children participated in the study. The mean IgG antibody level was 1.021 ± 0.9 IU/ml. Four hundred children (95.7%) had protective levels of antibodies. The highest proportion of subjects with protective levels was in infants, 6 - 11 months (99%) and lowest in children aged 36 - 47 months (92.2%). Conclusion: The proportion of children with protective levels was above 90% in all age groups studied. The current national immunization schedule is adequate. Further studies in older age groups are needful.