Age-appropriate vaccination coverage and its determinants in children aged 12–36 months in Nepal: a national and subnational assessment

Vaccination is one of the effective ways to develop immunity against potential life-threatening diseases in children in early age [1]. For instance, diseases such as polio and diphtheria are becoming rare in many countries around the world due to effective and timely vaccination [2, 3]. To reduce the risk of getting exposed to vaccine preventable diseases and to increase immunization coverage of basic childhood vaccines, World Health Organization (WHO) initiated the Expanded Programme on Immunization (EPI) in 1974. Remarkable progress has been made worldwide since the implementation of EPI [4, 5]. For instance, over the last decade, more than 1 billion children have been vaccinated and an estimated 2 to 3 million death has been averted through immunization worldwide [5, 6]. However, at the same time, nearly 20 million children still face insufficient access to vaccines globally [7‐9]. The resurgence of vaccine preventable diseases (VPD) such as measles in Mongolia, USA and in other countries has emphasized that not only coverage rate but also timeliness of the vaccines administered is important to ensure effective immunization [10‐13].

In Nepal, the National Immunization Program (NIP) was implemented in 1979 with the objectives to increase immunization coverage and control the vaccine-preventable diseases [14]. The immunization programme has performed well and has been considered success in recent years. In 2017, the crude vaccination coverage for most of the vaccines was reported above 80% [15]. However, the increasing cases of measles and high prevalence of tuberculosis in Nepal in recent years has posed an important question on the effectiveness of the immunization program [16, 17]. Currently, the surveillance report on immunization by WHO emphasized that the immunization program is solely focused on attaining high coverage rate while neglecting the timeliness of the vaccines administered [15]. Delay in immunizations may cause outbreaks of infectious disease since vaccines delivered outside the immunization schedule leave temporal gaps in immunity in which children are vulnerable to infections [18]. Hence, to realize the full benefits of immunization program, it is important to consider timely administration of the vaccines along with the high coverage rate. However, there are no studies been conducted at national level to access the timeliness of childhood vaccines in Nepal. Thus, this is the first study aimed to analyse the age-appropriate vaccination coverage at national and subnational levels and to identify the factors associated (compliance) with age-appropriate vaccination in Nepal.

Full benefits of vaccination could be attained through high coverage and timely administration. Nepal has already met the immunization target set by WHO to attain 90% coverage for most of the childhood vaccines. According to WHO/ UNICEF estimates of immunization coverage report 2019, the crude coverage for most of the vaccines were above 90% in Nepal. The 2018/19 annual report provided by the Health Ministry of Nepal reported that the crude coverage for some vaccines such as BCG was 92% [15]. However, according to our study findings, the age-appropriate coverage of BCG vaccine was below 60% at national level.

Although immunization program has been considered successful in Nepal with target coverage being met [23], low age-appropriate coverage of these vaccines remains a big issue. Several studies conducted in similar settings in different countries estimated low age-appropriate coverage of childhood vaccines [12, 20, 24‐27]. The recent increase in number of measles and tuberculosis cases in Nepal could be attributed to untimely vaccination in Nepal [17, 28]. The reasons behind the low age-appropriate vaccines coverage rate might include lack of awareness about the immunization schedule, hard to access health care facilities, reluctancy in administering vaccines, hesitancy of parents regarding vaccination, insufficient infrastructure to transport and store the vaccine in hard to reach areas, and occurrence of unusual events such as natural disaster, disease outbreak (pandemic situation) [20, 26, 27, 29‐33].

The huge earthquake of 2015 in Nepal significantly affected the healthcare services in different provinces throughout the country [34]. Our study was conducted after the earthquake. Therefore, it is highly possible that the 2015 earthquake could have a significant effect on health care facilities leading to delay in vaccination and resulting in low age-appropriate coverage. Similarly, it could be inferenced that Covid19 outbreak would affect the vaccination program in different regions and would increase the risk to the resurgence of VPD [35]. Therefore, to cope with the unforeseen circumstances such as natural disasters and disease outbreaks, the central government along with the local government should focus on capacity building for disaster preparedness, improve basic infrastructure, mostly in hard to reach areas, and strengthen community healthcare facilities. Furthermore, provincial governments should focus on planning and setting framework based on local situation at regional levels.

In this study we found that along with low age-appropriate coverage, the timely coverage of later doses of vaccines subsequently declines compared to the former doses. For instance, timely coverage of second and third doses of OPV and PE vaccines significantly decreases as compared to its respective first dose. This result is similar to those found in the neighbouring countries such as Bangladesh and Pakistan [26, 36]. One of the possible explanations for this could be increase in workload for mothers and increase in domestic activities while a child become older. Another explanation could be the adverse events such as fever, pain or swelling on the injection site, following the prior doses that would restrain mothers for the next appointment [37, 38]. Furthermore, parents’ perception that the later doses are not as important as the first dose, and reluctancy to follow up could explain the existing low age-appropriate coverage for later doses [29, 38].

At regional level, high disparity was observed in age-appropriate vaccination coverage. In Province 2 and Province 6, timely coverage of the vaccines included in this studied  was lower compared to that in other regions. Though, geographically Province 2 is easily accessible, the low vaccination coverage could be due to low compliance rate, low literacy rate, hesitancy towards vaccination, lack of knowledge about the immunization program, lack of proper health care infrastructure in rural areas, and other cultural barriers [39‐41]. Use of mobile phone/smart phone (mhealth) to improve the knowledge and awareness about vaccination and immunization schedule could be an effective way [42, 43]. In case of Province 6, low age-appropriate coverage could be due to hard to reach terrain, lack of awareness about the immunization schedule, lack of sufficient infrastructure such as transportation and storage facilities, and lack of human resource in health sector [32, 33]. Use of drones technology to transport vaccines in hard to reach areas could solve the problem in these regions [44]. Province 3 had the highest coverage of almost all the vaccines as it is the central region that includes capital city Kathmandu, and most of the areas in this province are developed [19, 41].

As highlighted in the previous study [20], the analysis of vaccine data using the DHS has several limitations. First, only children who had vaccination records in the mother and child health book (the vaccination card) were included. Due the exclusion of children who did not have the vaccination card, the sample size has reduced to 460 which is not a large sample size for this study hence posing a limitation to the study. In addition, exclusion of children without vaccination records might lead to overestimation of the vaccination coverage and timeliness if these children were less likely to receive adequate vaccinations. Children who were excluded from our analyses due to missing data on vaccination were more likely to be from the poorest household as compared with those included in the study. Second, age-appropriate vaccination coverage among children can be influenced by many other factors, including those related to access to health care services, knowledge, attitudes, and practices of parents and providers. The variables investigated in this study were limited to those available in DHS. Third, due to significant missing data and long administration period (between 4 to 6 years of age) of second dose of MMR vaccines we could not include it in the study. Finally, both early and delayed vaccinations were analyzed as a single category. Investigation of each of these types of untimely vaccinations is a topic for future studies.

This is the first national level study conducted in Nepal focusing on the timeliness of childhood vaccination. Our study showed that although the crude coverage of childhood vaccines is above 90%, the age-appropriate coverage of these vaccines is significantly low at national and subnational levels. The national immunization program is solely focused on attaining high crude coverage while neglecting the importance of timeliness of the vaccines administered. The significantly low age-appropriate coverage of all the childhood vaccines at national and subnational level emphasizes the importance of formulating effective policies at national and subnational levels to improve the age-appropriate coverage rate. Increased focus on promoting awareness about the immunization schedule in several regions, particularly, in the provinces with significantly low age-appropriate coverage (Province 2 and Province 6) is of prime importance.