Seroprotection against tetanus in southern Vietnam

Abstract

Background: Ongoing tetanus cases and sporadic outbreaks of vaccine-preventable diseases associated with routine vaccination programmes remain problems in many low and middle-income countries, including Vietnam. With no human-to-human transmission or natural immunity, tetanus antibody levels indicate both individual risk of tetanus and gaps in vaccination programmes.

Methods: To investigate gaps in immunity to tetanus in Vietnam, a country with a historically high level of tetanus vaccination coverage, tetanus antibodies were measure by ELISA from samples selected from a long-term serum bank, established for the purposes of general-population seroepidemiological investigations in southern Vietnam. Samples were selected from 10 provinces, focussing on age-groups targeted by national vaccination programmes for infants and pregnant women (Expanded Programme on Immunization, EPI, and Maternal and Neonatal Tetanus, MNT).

Results: Antibodies were measured from a total of 3864 samples. Highest tetanus antibody concentrations occurred in children under 4 years old, over 90 % of whom had protective levels. Approximately 70 % of children aged 7-12 years had protective antibody concentrations although there was variation among provinces. For infants and children, there were no significant differences in tetanus protection between males and females, but for adults aged 20-35 years, in five of the ten provinces surveyed, protection against tetanus was higher in females (p < 0.05) who are eligible for booster doses under the MNT programme. In seven of ten provinces, antibody concentrations were inversely related to age (p < 0.01) and protection of older individuals was generally low.

Conclusion: Widespread immunity to tetanus toxoid is seen in infants and young children consistent with the high coverage rates reported for diptheria tetanus toxoid and pertussis (DTP) in Vietnam. However, the lower antibody concentrations seen in older children and men suggest reduced immunity to tetanus in populations not targeted by EPI and MNT programmes.

Keywords: EPI; Low middle income country; Seroprotection; Tetanus; Vaccination; Vietnam.

Fig. 1

Map showing number of samples collected from each site in southern Vietnam.

Fig. 2

Anti-tetanus toxin antibody concentrations in 3 selected age groups. Top: < 4 years old; middle:7–12 years old and bottom, 20–35 years old, disaggregated according to sex, females (red) and males (blue). All points plotted in green, red, or blue. Boxplots show medians and interquartile (IQR) ranges and whiskers show 1.5 times the IQR. In the bottom panel, p-values are shown where IU/ml values are significantly different between men and women. Yellow triangles show geometric mean IU/ml value for each subsample. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Antibody concentration for the 20–80 year age group by province with 95 % confidence intervals (shaded area) produced using LOESS regression .