Vaccines have the biggest success stories in the field of public health. Childhood immunization against vaccine-preventable diseases (VPD) is recognized as one of the most cost-effective programs to diminish childhood mortalities and morbidities across the world [1
]. Every year, vaccination against VPDs prevents childhood illness, disabilities, and saves millions of children’s lives around the world [3
]. It was estimated that, between 2010 to 2015 at least 10 million deaths were prevented globally and millions of more lives were protected from sufferings and disabilities associated with many infectious diseases [4
]. Over the decades, remarkable improvements have been made toward the development of national immunization programs. Expanded Program on Immunization (EPI) of World Health Organization (WHO) has the major contribution to this global success [5
]. EPI is a routine activity within the public healthcare system including mass immunization campaigns and door-to-door activities across the country aiming to increase the routine vaccine uptake. EPI was formally established in 1974 targeting childhood immunization against six vaccine-preventable diseases (i.e., diphtheria, pertussis, tetanus, poliomyelitis, measles, and tuberculosis) by 1990 [6
]. Implementation of EPI has increased the vaccine coverage globally; in 2017 EPI achieved around 85% DPT (3 doses of diphtheria-tetanus-pertussis) coverage worldwide with 123 countries of at least 90% coverage. The global coverage of measles and polio was also high as near to 85% for both by the end of 2017 [7
Along with the global success, Senegal also achieved significant improvements in the child immunization coverage and reduction of child morbidity and mortality. Senegal launched its EPI in 1979 with the support of international donors targeting immunizing against seven childhood diseases which was later increased to 11 in 2005 [8
]. EPI program in Senegal recommends that a child should receive BCG (Bacillus of Calmette–Guerin) vaccine against tuberculosis soon after birth, oral polio vaccine (OPV), and the monovalent pneumococcal conjugate vaccine (PCV) at birth and at 6th, 10th and 14th week, and at 9th month. Since 2005, DPT vaccine had been replaced by pentavalent vaccine which contains a combination of five vaccines in one dose i.e., diphtheria, tetanus toxoid, pertussis, hepatitis B, and Hemophilus influenza type b vaccine (Hib) and recommended to be administered at the same time as the OPV or PCV at 6th, 10th, and at 14th week from birth (Table 1
]. Since measles is highly endemic and frequently affects infants in Senegal, routine measles vaccination is recommended at the 9th month of age with a second dose at 15th month. Additionally, a dose of yellow fever is also given at the age of nine months [9
]. Regardless of successes, vaccine-preventable diseases are the leading cause of childhood mortality in Senegal while the under-five child mortality rate is still high as 45 per 1000 live births [11
]. Further, the country experienced a rise in measles incidence in 2009 with high case fatality rate which indicates the necessity of increasing efforts in achieving full immunization coverage among children [12
Utilization of healthcare services including immunization is a complex phenomenon involving health service providers, cultural beliefs, parent’s characteristics and socio-economic factors, and even the geographic barriers [14
]. It is well recognized that full immunization coverage and broader socio-economic benefit of immunization are interrelated. However, such benefits of immunization are not yet achieved in many West African countries including Senegal, as the coverage of full immunization among children is below the national and international target and even not equally distributed across geographic regions and ethnic groups [8
]. Therefore, it is crucial to identify the various factors that may influence children to be fully immunized. Although immunization coverage rate and associated factors are the emerging global health topics in many countries, limited studies are available in the context of Senegal. A number of studies have reported their findings on child immunization coverage but few of them generated evidence about the socio-demographic factors associated with full immunization among children. However, the existing studies focused on either specific target areas (e.g., urban, rural, geographic location), among younger aged children or on certain vaccine-preventable diseases [10
]. Also existing studies are unable to present the current scenario of full immunization coverage as these studies often used either previous round data or not representative of the country scenario of full immunization status. Although a recent study served the need for documenting full immunization coverage and its determining factors to a great extend, however, this study also needs to monitor the change of immunization coverage and determining factors over time as it utilized the latest Demographic and Health Survey (DHS) 2017 dataset for analysis [8
]. We hypothesize that the current immunization coverage rate and their determinants will potentially help to serve the purpose of launching Continuous-DHS program by providing up-to-date information to the policy makers for planning, monitoring, and evaluating national EPI program to manage vaccine-preventable diseases in an effective manner.
Although substantial improvement have been made for protecting Senegalese children from violence, poverty, and child labor, children’s health still remain a serious public health problem [22
]. Childhood immunization is one of the most effective public health interventions for diminishing the burden of disease among young children in resource-poor settings. The present study examined the status of full immunization coverage among 12–36 months aged children and determinants of full immunization status. The study observed that the overall full immunization coverage was 70.96% which is low compared to the global immunization coverage, but better than many African countries [23
]. Several factors such as regional variation, ethnicity, number of ANC and PNC received, mother’s age at delivery, access to mass media, and wealth index have the significant association with full immunization status. There were also some other crucial factors such as, area of residence, birth order, place of delivery, parental education, and distance to health care facility which were significantly associated with the uptake of full dose vaccines independently.
Despite the success, full immunization coverage varies across the country and among the type of vaccines. Our study observed a seven percentage point decline in coverage of immunization from BCG at birth (95.33%) to measles (88.69%) to be administrated after nine months of birth. Similar findings were also found in earlier studies, however, this coverage gap has been reduced over time [8
]. This finding indicates the prevalence of missed opportunities and the challenge of introducing measles vaccine routinely after the ninth month of birth. Therefore, more promotional activities and actions are needed to increase the consciousness among the guardians for the uptake of all the essential vaccines. A recent study showed the consequence of low measles vaccine coverage in Europe despite of their socio-economic strata [24
]. Reason behind lower uptake rate of measles vaccine may be because of the experience of adverse effect of earlier vaccines, failure to remember or understand the schedule of routine immunization, or because of less awareness or guidance from health professionals [25
]. Our study found differences in full immunization coverage rate across different geographic regions and ethnic groups. For instance, children from the western region and children from the Serer ethnic group had the highest rate for full immunization coverage compared to others. Such geographical disparities in the coverage of full immunization were also found in many low and middle-income countries [19
]. This difference may be due to various supply side factors such as distance, quantity and the quality of health-care services, fragile service delivery, and communication system, and also demand side factors such as, differences in the religious conservatism, fear of side effects, and the acceptance of immunization services based on cultural beliefs or differences [28
]. Therefore, policy should target the low coverage regions considering the both supply and demand side barriers.
Apart from the effect of geographic regions and ethnic groups, accessibility to maternal health-care services i.e., antenatal and postnatal care (ANC and PNC) was also found to be the influencing factors for full immunization coverage. Like earlier findings, we also observed that mothers who utilized recommended ANC and PNC services were most prone to fully vaccinate their children [8
]. This may be explained by the fact that during the ANC and PNC visits, mothers receive enough positive information about childhood vaccination which make them confident about their child’s preventive health. Besides, from the unadjusted model, we observed that distance to health facility was also a significant factor for the uptake of all the recommended vaccines. This finding was confirmed by an earlier study from a developing country where it was shown that walking or travelling time, transport facility, and distance are the key factors that influence the utilization of healthcare services and walking distance more than 30 min diminishes the uptake rate of vaccines by one-third [20
]. Full immunization rate was also found to increase with the increase of parental educational attainment and maternal age at the time of delivery. Like other studies in various settings, we also observed a positive association between the parental education and full immunization coverage, which indicate that knowledge and awareness on preventive care is crucial for the uptake of vaccines [19
]. Therefore, community-based behavior change program such as broadcasting motivational and awareness-developing programs on radio, television, staging informative drama, and announcing through mikes should target the uneducated mothers for the better understanding of the beneficial role of immunization so that they will be encouraged to vaccinate their children timely.
Wealth status of the households played a significant role in immunizing their children. Our results are in similar line with various studies indicating that the chance of being fully immunized is positively associated with households’ wealth status [19
]. Although immunization services was completely free of charge, indirect cost of vaccination such as income loss and transportation cost might be incurred which appeared as an additional economic burden for the poorest households [31
]. From the univariate analysis, we found that full immunization was better among urban children than the rural, which was confirmed by other earlier studies [19
]. This is due to the large number of quality health facilities that are available in most of the urban areas compared to rural, however, such relationship was not observed in multivariate analysis.
In accordance with various studies in different settings, healthcare decision-making ability was found as an important factor for full immunization coverage [19
]. We have found that, if mothers are the decider of their self-healthcare then the children are more likely to be fully immunized and vice versa. This might be due to the health consciousness and autonomy in decision-making that triggers mothers to be concerned about their children’s health care and so as vaccine uptake also. Thus, community-based behavior change programs targeting parents might be helpful to be aware of their child immunization.
The study has several limitations. The study is based on secondary data and for few cases immunization records were obtained as the mother stated. Therefore, the potential effect of recall bias on our results cannot be ignored. Nonetheless, mother’s report is considered as the valid measure of immunization coverage in the absence of a health card [34
]. Further, the explanatory variables were selected based on similar previous studies and upon availability in DHS dataset, however, there might be some other potential predictors of full immunization which was unable to capture. Despite such limitations, current study is based on the latest continuous nationally representative survey which presented the national representative immunization scenario of Senegalese children. Therefore, the findings are still noteworthy and relevant in drawing attention to the health policy makers for ensuring the benefit of vaccination for the betterment of child health.