Objective  To understand the diphtheria antibody levels in the healthy population in Karamay city, Xinjiang Uygur Autonomous Region.

Methods A questionnaire survey was conducted among healthy individuals who had lived for more than 6 months in four districts of Karamay city by the convenience sampling method. Venous blood was collected, and the diphtheria immunoglobulin G (IgG) antibody level in the serum was measured by enzyme-linked immunosorbent assay (ELISA). Statistical analysis was conducted by rank sum test and χ² test.

Results A total of 3 508 participants were included in the study. The median concentration, positive rate, and protection rate of diphtheria IgG antibodies were 0.13 IU/mL, 99.97% and 58.07%, respectively. Differences in gender, district, age interval, and history of diphtheria vaccination caused differences in median concentration of diphtheria IgG antibodies (H values were 149.55, 21.29, 1 199.38, and 1 105.23, respectively, all P < 0.01) and protection rates (χ² values were 113.19, 19.15, 1 002.40, and 967.08, respectively, all P < 0.01). Among the 2 155 children and adolescents who had received ≥ 4 doses of a vaccine containing diphtheria components, the median concentrations of diphtheria IgG antibodies were 0.28, 0.17, 0.24, 0.18, and 0.21 IU/mL for those with vaccination durations of 6–23 months, 2–4 years, 5–7 years, 8–10 years, and 11–16 years respectively (H = 96.68, P < 0.01), and the antibody protection rates were 91.76%, 67.77%, 79.84%, 72.73%, and 77.68% respectively (χ² = 67.50, P < 0.01).

Conclusions The overall diphtheria antibody level is high in the healthy population of Karamay city, and the level in the age group of < 18 years old is much higher than that in the age group of ≥ 18 years old. The implementation of the national immunization program for children of the appropriate age has a significant effect of preventing diphtheria in children. In the future, booster immunization with diphtheria-containing vaccines for adults should be considered.