Seroepidemiology of diphtheria and tetanus among children and young adults in Tajikistan: Nationwide population-based survey, 2010

Background

Tajikistan had a major diphtheria outbreak (∼10,000 cases) in the 1990s, which was controlled after nationwide immunization campaigns with diphtheria-tetanus toxoid in 1995 and 1996. Since 2000, only 52 diphtheria cases have been reported. However, in coverage surveys conducted in 2000 and 2005, diphtheria-tetanus-pertussis vaccine coverage was lower than administratively reported estimates raising concerns about potential immunity gaps. To further assess population immunity to diphtheria in Tajikistan, diphtheria antibody testing was included in a large-scale nationwide serosurvey for vaccine-preventable diseases conducted in connection with a poliomyelitis outbreak in 2010. In addition, the serosurvey provided an opportunity to assess population immunity to tetanus.

Methods

Residents of all regions of Tajikistan aged 1–24 years were included in the serosurvey implemented during September–October 2010. Participants were selected through stratified cluster sampling. Specimens were tested for diphtheria antibodies using a Vero cell neutralization assay and for tetanus antibodies using an anti-tetanus IgG ELISA. Antibody concentrations ≥0.1 IU/mL were considered seropositive.

Results

Overall, 51.4% (95% CI, 47.1%–55.6%) of participants were seropositive for diphtheria and 78.9% (95% CI, 74.7%–82.5%) were seropositive for tetanus. The lowest percentages of seropositivity for both diseases were observed among persons aged 10–19 years: diphtheria seropositivity was 37.1% (95% CI, 31.0%–43.7%) among 10–14 year-olds, and 35.3% (95% CI, 29.9%–41.1%) among 15–19 year-olds; tetanus seropositivity in respective age groups was 65.3% (95% CI, 58.4%–71.6%) and 70.1% (95% CI, 64.5%–75.2%).

Conclusions

Population immunity for diphtheria in Tajikistan is low, particularly among 10–19 year-olds. Population immunity to tetanus is generally higher than for diphtheria, but is suboptimal among 10–19 year-olds. These findings highlight the need to improve routine immunization service delivery, and support a one-time supplementary immunization campaign with diphtheria-tetanus toxoid among birth cohorts aged 1–19 years in 2010 (3–21 years in 2012) to close immunity gaps and prevent diphtheria outbreaks.