Our objective was to assess trend and inequalities in full immunization coverage of infants in Nepal using three recent DHS data. Our results show that full immunization coverage increased from an average of 83% during 2002-2006 to 88% during 2007-2011, then it decreased to 78% during 2012-2016, with the adjusted annual decrement of 22% (95% CI: 6%-36%). However, children born to the poorest households saw an increase in full immunization coverage to 76.6% during 2012-2016 from 68% during 2002-2006, with inequity in full immunization coverage reducing over time in terms of rich: poor ratio, rich-poor difference and concentration indices and confirmed by Lorentz curve. The decrease in pro-rich inequalities from 2002 to 2016 was partly attributable to a substantial decrease in full immunization coverage among the children from the wealthier quintiles and a slight increase among children from the lowest income quintile. A significant declining trend in full immunization coverage in Nepal, albeit retention of equity gain among the children from households with poorest wealth quintile, puts Nepal's immunization program far behind GoN's target to fully immunize more than 90% of children by 2020(3). Nepal's experience of the significant simultaneous decline in overall full immunization coverage together with a decline in pro-rich inequity is similar to that experienced by the Central African Republic(8).
A similar study by KC et al. (7) used data from the Demographic and Health Surveys carried out in 2001, 2006, 2011 and MICS 2014 showing that the poorest wealth quintile with the most significant improvement in immunization coverage, from 58% in 2001 to 77.9% in 2014 while the wealthiest quintile showing a little improvement from 84.8% to 86.0% . The study also found improving slope index of inequality for children who received all vaccines improved from 0.070 (95% CI: 0.061–0.078) to 0.026 (95% CI: 0.013–0.039) and relative index of inequality from 1.13 to 1.0. The authors attributed the improvement in immunization coverage between 2001 and 2014, mainly to the interventions targeting the disadvantaged populations. Case studies from 10 of 75 countdown countries, also showed an increased coverage for interventions administered at lower levels of the health system including immunization, along with reduced equity gaps and improvements in associated health outcomes during the MDG era(17).
The steady improvement in full immunization coverage, as shown by NDHS 2006(11) and NDHS 2011 (12), and decreased equity gap, (by wealth, education and caste), can be attributed to the concentrated efforts of the GoN in collaboration with non-governmental organizations and local community, to focus on hard-to-reach and disadvantaged populations (18). However, full immunization coverage declined after the 2011 DHS survey mainly due to decline in DPT3 coverage. KC et al. reported similar findings where the decline in DPT3 and polio vaccine were the main contributor to the decrease in full immunization coverage(7). Phase-out of community health workers' position such as Village Health Workers might have affected immunization service utilization since direct communication through the household visit by health workers had a positive impact on immunization service utilization (15, 19). However, the decline in full vaccination coverage, mainly driven by the decline in DPT3 coverage is difficult to interpret. The decline may be due to health system factors such as changes in national immunization program and the introduction of new vaccines (PCV, IPV, MR, JE). Logistics and supply chain management issues after the introduction of new vaccines contributed to the decline in DPT3 coverage in South Africa in 2009(20). Other possible explanation could be due to mothers' and their newborns' temporary move to her mother's house(21) around 10-14 weeks of childbirth and less familiarity with vaccination schedule, and place in the new place. Another reason may be people's perception of not feeling the importance of three doses of vaccine after one or two doses of the same vaccine has already been received. It may also be associated with a reduced feeling of threat against polio(7) since DPT and polio are administered simultaneously at 6,10 and 14 weeks. However, this needs further investigation.
Further analysis of NDHS 2016 showed the main reason for the significant decline in full vaccination to be the decline in the percentage of children who received the third dose of DPT containing vaccine from 91.7% in 2011 to 85.9% in 2016(14). The drop out in the third dose of DPT is an increase from 5% (95% CI 3.1-7.6) in 2011 to 11% (95% CI 8.8-13.8) in 2016. However, the coverage of measles-containing vaccine, which is provided after the third dose of DPT, has increased from 88.0% in 2011 to 90.4% in 2016, suggesting a missed opportunity for vaccination of DPT3 at nine months. Also, vaccination card was retained by just over half of the mothers (52.3%) (13). Card retention was one of the factors associated with full immunization coverage, along with the place of delivery (14). In their analysis, geographic and urban/rural place of residence were not associated with differences in full immunization coverage. However, current analysis using recent three NDHS demonstrated the decreasing trend in full immunization coverage over last 15 years to be significant for children living in rural areas, Terai region and in province 2(Table 3). While an increase was observed among most disadvantaged Caste/ethnicity ‘Dalits,' other relatively disadvantaged castes/ethnicity groups such as " Terai/Madhesi and Muslim/others” saw a decreasing trend. The more substantial decline in caste groups primarily residing in the Terai region requires further ethnographic exploration. In addition, the reason for the statistical difference in annual coverage among specific population groups may be partly due to a more substantial relative change in full vaccination coverage (increasing and then decreasing) between 2002 to 2016. It could also be due to health service or health belief related factors not included in DHS data.
We analyzed factors associated with a continuously decreasing trend in immunization coverage in province 2. Surprisingly, only maternal education was the independent predictor of full immunization coverage in province 2, and wealth quintile did not make any difference. Maternal education was found to be a strong predictor of immunization uptake in Nepal (7) and other settings (22).
The overall decline in full immunization coverage, coupled with a significant declining trend among the rich income quintiles has multiple implications. In one hand, as the coverage of full immunization starts to decline, the momentum of pro-poor equity gain may be reversed, and poor and disadvantaged groupswill be most likely to be missed out. On the other, a significant declining trend of full immunization coverage among rich income quintiles needs an urgent investigation and timely action. A study from Nepal has shown that improving the quality of the vaccination program maybe even more important than improving access to it (19). While improving access is essential to reach some sections of the populations, improving service quality is equally important.
Strengths and Limitations
We used nationally representative data from the DHS survey. Furthermore, we merged dataset from 3 recent DHS surveys conducted in 2006, 2011, and 2016, which increased the power of our regression analyses. We also used three inequality indicators, namely the ratio between Q5 and Q1, the rich-poor difference, and the concentration index for the analysis of equity gaps in full immunization coverage. However, the study has some limitations. Only six antigens administered during the infancy were considered for comparison of coverage over the years because some of the antigens recently introduced were not available during the period covered by earlier surveys conducted in 2006 and 2011.
Additionally, no supply-side factors were included in the models since DHS data lacks health service-related data. Variables related to socio-cultural practices, social norms, and beliefs regarding immunization were not available. Furthermore, we included income quintiles as a proxy measure of socioeconomic status. However, multiple aspects of poverty might reflect SES better than income quintiles. When vaccination cards were not available, interviewers relied on mothers' reports to determine receipt of immunization. Therefore, misclassification could have arisen if mothers did not correctly recall the name and receipt of the vaccine.