Diphtheria and tetanus seroepidemiology among children in Ukraine, 2017

Abstract

Background: The drastic decline of Ukraine's immunization coverage since 2009 led to concerns about potential resurgence diphtheria and tetanus, along with other vaccine-preventable diseases.

Methods: To assess population immunity against diphtheria and tetanus, we tested specimens from the serosurvey conducted in 2017 among children born in 2006-2015, the birth cohorts targeted by the nationwide outbreak response immunization following a circulating vaccine-derived poliovirus type 1 outbreak in Zakarpattya province in 2015. We surveyed four regions of Ukraine, using cluster sampling in Zakarpattya, Sumy, and Odessa provinces and simple random sampling in Kyiv City. We tested serum specimens for IgG antibodies against diphtheria and tetanus, using microbead assays (MBA). We estimated seroprevalence and calculated 95% confidence intervals. We also obtained information on the immunization status of surveyed children.

Results: Seroprevalence of ≥0.1 IU/mL diphtheria antibodies was <80% in all survey sites (50.0%-79.2%). Seroprevalence of ≥0.1 IU/mL tetanus antibodies was ≥80% in Sumy, Kyiv City, and Odessa (80.2%-89.1%) and 61.6% in Zakarpattya. Across the sites, the proportion of children vaccinated age-appropriately with diphtheria-tetanus-containing vaccines (DTCV) was 28.5%-57.4% among children born in 2006-2010 and 34.1%-54.3% among children born in 2011-2015. The proportion of recipients of <3 DTCV doses increased from 7.1%-16.7% among children born in 2006-2010 to 19.8%-38.6% among children born in 2011-2015, as did the proportion of recipients of zero DTCV doses (2.6%-8.8% versus 8.0%-14.0%, respectively).

Conclusions: Protection against diphtheria among children born in 2006-2015 was suboptimal (<80%), particularly in Zakarpattya. Protection against tetanus was adequate (≥80%) except in Zakarpattya. Diphtheria-tetanus immunization status was suboptimal across all sites. Catch-up vaccination of unvaccinated/under-vaccinated children and other efforts to increase immunization coverage would close these immunity gaps and prevent the resurgence of diphtheria and tetanus in Ukraine, particularly in Zakarpattya.

Keywords: Diphtheria; Diphtheria antibodies; Diphtheria-tetanus multiplex bead assay (MBA); Diphtheria-tetanus vaccination coverage; Multiplex bead assay (MBA); Seroepidemiology; Seroprevalence; Tetanus; Tetanus antibodies; Ukraine; WHO European Region.

Figure 1.. Immunization coverage in Ukraine, 1990–2019

Source –Official country reports submitted to WHO, except for 2009, 2013, and 2014 [3]. No reports were submitted to WHO for those years. Therefore, WHO/UNICEF estimates are used. DTP3, third dose of diphtheria, tetanus, pertussis-containing vaccine; MCV1, first dose of measles-containing vaccine; MCV2, second dose of measles-containing vaccine; Pol3, third dose of polio vaccine; HepB3, third dose of hepatitis B vaccine; HepB_BD, birth dose of hepatitis B vaccine

Figure 2.. Reported cases of diphtheria (1990–2019) and tetanus (1995–2019) in Ukraine

Source – Country reports submitted to WHO [1, 2]. No reports were submitted for diphtheria in 2009, 2013, and 2014; for tetanus in 2005, 2009, 2013 2014, 2015, and 2017

Figure 3.. Sites included in the serosurvey for vaccine-preventable diseases — Ukraine, 2017

The designations used and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of WHO concerning the legal status of any country, territory, city or area, or of its authorities, nor concerning the delimitation of its frontiers or boundaries.

Figure 4.. Diphtheria and tetanus antibody levels among children born in 2006–2015 by age group and survey site — Ukraine, 2017

Antibody levels <0.01 IU/mL correspond to no protection, 0.01–0.09 IU/mL – to minimal protection, and ≥0.1 IU/mL to full protection, including 0.1–0.9 IU/mL, linked to shorter-term protection, and ≥1.0 IU/mL, associated with long-term protection.