The trend of full vaccination coverage
Our results show that full immunization coverage steadily increased from 65.6 % in 2001 to 87.0% in 2011, but decreased to 77.8% in 2016.The trend was significant over time. Further analysis of NDHS 2016 showed the main reason for the significant decline in full vaccination to be the decline in the percentage of infants who received the third dose of DPT containing vaccine from 91.7% in 2011 to 85.9% in 2016(20). The drop out in the third dose of DPT increased from 5% (95% CI 3.1-7.6) in 2011 to 11% (95% CI 8.8-13.8) in 2016. However, the coverage of the 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.
KC et al. reported similar findings among under-five infants where the decline in DPT3 and polio vaccine were the main contributor to the decrease in full immunization coverage(10). Phase-out of community health workers' positions 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 (21, 26). 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 the national immunization program and the introduction of new vaccines in different regions of the country (DPT-HepB-HiB, Pneumococcal conjugate vaccines(PCV), Inactivated Polio Vaccine(IPV), Measles-Rubella(MR), and Japanese Encephalitis(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(27). Other possible explanation could be due to mothers' and their newborns' temporary move to her mother's house(28) 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(10) since DPT and polio are administered simultaneously at 6,10 and 14 weeks. However, this needs further investigation.
When analyzed among the pooled sample from all four NDHS years, urban residence, residence in Province 2, no maternal education, and lower household wealth quintile were found to be associated with significantly lower coverage of full immunization among infants. Despite geographical accessibility, Province 2 has the lowest women literacy in Nepal(29), health facilities had lower performance in child health care(30) and have socio-cultural barriers compared to other provinces of Nepal. Our findings of higher full vaccination coverage among infants from richer families and those born to mothers with higher educational status are consistent with studies from Ethiopia and Bangladesh(31, 32). Women from wealthy families may be more likely to accept "modern/medical" services than their poor counterparts(31). Similarly, mothers with higher educational status might be aware of the preventive role of immunization service compared to women with no education. A meta-analysis on the role of maternal education on childhood vaccination also showed that maternal education plays a more important role in lower-income countries than in high-income countries (33).
Equity Gap in full vaccination coverage
Increased full immunization coverage from 2001 until 2011 and a recent decline in full immunization coverage in 2016, overall showed a narrowing equity gap by wealth quintiles and maternal educational status. The absolute inequalities in full immunization coverage saw a drop over time by educational status and wealth quintiles. The Relative Index of inequality also showed an improvement over time, both for wealth quintile and for maternal education between 2001 and 2016. A similar study among under-five children by KC et al. (10) used data from the DHSs 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 the slope index of inequality for infants 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 decreased equity gap (by wealth, education) can be attributed to the concentrated efforts of the GoN in collaboration with non-governmental organizations and the local community, to focus on hard-to-reach and disadvantaged populations (34).
A significant decline in full immunization coverage in Nepal after 2011, albeit retention of equity gain among the infants from households with poorest wealth quintile and those with no education, 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(12). Case studies from 10 of 75 countdown countries selected for measuring progress against MDG 2015 targets 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(35).
Policy, Practice and Research implications
Although this study did not investigate health system factors affecting service utilization, the findings from Acharya et al. 's analysis of much lower coverage of DPT3 compared to DPT1 and DPT2(20)partly indicate health system's weakness to retain service users. Furthermore, lower DPT3 coverage than measles coverage clearly indicates a missed opportunity to utilize children's contact with the health system. First of all, text messages or reminders/recalls or other systems need to be in place to remind/follow up(36)parents to ensure full vaccination on time. Second, there should be a mechanism to provide missed vaccines when children come in contact with the health system for other services in the future.
A higher decline in full immunization observed among infants born to mothers from middle and the highest income quintiles may have different reasons. An earlier study from Nepal has shown that improving the quality of the vaccination program maybe even more important than improving access to it (26). While improving access is essential to reach some sections of the population, improving service quality may be more important to retain wealthy families. Higher waiting time associated with staff shortage and increased number of new vaccines might have discouraged wealthy families to complete the full immunization. Therefore, a higher declining trend of full immunization coverage among middle and rich income quintiles needs an urgent investigation and timely action. As the coverage of full immunization starts to decline, the momentum of pro-poor equity gain may be reversed, and poor and disadvantaged groups will be most likely to be missed out. Altogether, these findings highlight the need to focus on reaching the poor without forgetting the richer sections.
Our analysis showed that although in decreasing trend, inequalities in full immunization coverage persist by maternal educational status and household wealth quintiles with service utilization concentrated among those in higher wealth quintiles and those with higher education. Furthermore, the recent decline in full immunization coverage after 2011 was higher among infants born to mothers with no education with respect to infants born to mothers with higher education, which led to a spike in crude difference from 14.3% in 2011 to 23.4% in 2016 (Table 4). Additionally, values of SII and RII were higher for maternal educational status compared to household wealth quintile for all DHS surveys indicating that there is a larger inequality by maternal education status than by household wealth status. Furthermore, absolute inequality declined significantly over time for wealth quintiles, compared to maternal educational status. Since maternal education was found to be a strong predictor of immunization uptake in Nepal (10) and other settings (37), these findings suggest that infants born to women with no or less education need special targeting to increase full immunization coverage. More importantly, all levels of governments in Nepal need to devise policies to promote girls' educational status since it has multiple returns on social, health, and economic sectors(38).
Strengths and Limitations
We used nationally representative data from the four most recent DHS surveys. Furthermore, we merged these datasets, which increased the power of our regression analyses. We also used both the absolute and relative measures of inequality for the analysis of equity gaps in full immunization coverage. And, we did this for wealth quintile as well as for maternal education, which are strong determinants of 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 studied 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 socioeconomic status 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.