Background
Childhood immunization still remains one of the most cost-effective preventive strategies against mortality and morbidity among children [
1]. Immunization saves the lives of up to three million children’s every year. High rates of vaccine coverage could prevent an additional 1.6 million deaths a year among children under the age of five [
1,
2].
Following WHO efforts to eradicate smallpox and control childhood diseases, Senegal launched its Expanded Programme on Immunization (EPI) in 1979. The goal of the national EPI is to ensure full immunization of children against preventable diseases. EPI is a routine activity within the public healthcare system. In addition, time specific mass immunization campaigns and door-to-door activities are regularly implemented across the country to help increase routine immunization uptake.
At the beginning of the program in 1979, the national EPI targeted seven diseases. The number of diseases covered later on increased to 9 in 2002, and then to 11 in 2005. The current immunization schedule for children 0 to 15 months old is shown in Table
1.
Table 1
Vaccine, year of introduction, and recommended immunization schedule in Senegal
BCG | 1979 | 1 | Soon after birth |
Polio 0a
| 1988 | 1 | |
OPVo: Soon after birth |
IPV | 2015 | 3 | IPV1: at 6 weeks IPV2: at 10 weeks IPV3: at 14 weeks |
Hepatitis B | 2016 | 1 | Within 24 h after birth |
Pentavalent vaccine | | | Penta 1: at 6 weeks |
2005 | 3 | Penta 2: at 10 weeks |
| | Penta 3: at 14 weeks |
PCV | 2013 | 3 | Pneumo 1: at 6 weeks |
Pneumo2: at 10 weeks |
Pneumo 3: at 14 weeks |
Measles and Rubella | 2014 | 1 | 9 months |
Rotavirus | 2014 | 2 | Rota1: at 6 weeks |
Rota2: at 10 weeks |
Yellow fever | 1988 | 1 | At 9 months |
Measles and Rubella | 2014 | 1 | Second dose at 15 months |
In Senegal, EPI is funded by the government and its partners (GAVI, UNICEF, and WHO) and vaccines are provided free of charge in public health facilities. Overall, the total cost of the routine immunization program in 2013 was $17,162,250 (USD) [
3]. However, despite the large sums spent to purchase vaccine the country is still struggling to maintain a steady and high rate of immunization coverage. In 2010, the reported global immunization coverage dropped down to 70%, with some districts reporting rates ≤50% for some specific vaccines. Additionally, in 2012 up to 14,940 infants did not even receive a single dose of BCG vaccine while many areas faced low use of immunization services with a DTP3 coverage between 50 and 79% [
4]. The country experienced within the last 5 years a rise in measles outbreaks with high case fatality rate [
5].
The breakdowns of the program are probably due to the fact that childhood immunization is a complex process involving health services organization, cultural beliefs, parent’s characteristics and socio-economic factors [
6]. Beyond the financial investment, national EPI programs should integrate in a coherent approach all the modifiable factors that can affect the immunization process. Moreover, implementing a sustainable immunization program requires also a reliable cold chain and transport systems, with adequate training of health workers and appropriate educational programs to inform the communities, mothers and caregivers about available services [
6].
In Senegal, most of the studies on childhood immunization focused on specific areas or on a small number of vaccine-preventable diseases [
5,
7,
8]. In addition, these studies mainly studied individual characteristics rather than determinants related to access to health care and environmental factors. Finally, existing research did not sufficiently use nationally representative household surveys to assess full immunization coverage and its determinants in the country.
Thus, we conducted a secondary analysis of the 2010–2011 Demographic and Health Survey (DHS) to assess routine immunization uptake and factors associated with full immunization among children aged between 12 and 23 months. A better understanding of these determinants might help the national EPI program to re-orient its approaches with new strategies that may further reduce mortality and morbidity among children in Senegal.
Discussion
We assessed routine immunization uptake and factors associated with full immunization among 12–23 months old children in Senegal. Our results show that among these children more than half of them received the nine recommended vaccines and the overall immunization coverage was 62.8%. Based on mother’s recall, 77.14% of children were vaccinated while only 37.5% were fully immunized based on information from the vaccination card. We found that children aged between 12 and 23 months whose mother showed a vaccination card, attended at least a secondary education level, attended antenatal care, or delivered at a health facility were more likely to be fully immunized. Moreover, children living in eastern regions were less likely to be immunized or complete their vaccination schedule when compared to children living in western regions.
The coverage of 62.8% felt short below the global immunization goal and strategy (GIVS) recommended target of ≥90% national immunization coverage set by WHO and UNICEF. However, this prevalence is still high when compared to what is seen in other West African countries such as Guinea: 30% [
3], Ivory Cost: 51% and Mali: 39% [
18]. The variations in immunization coverage between different countries can be explained by factors such as socio-cultural, or health services coverage and performance differences [
6].
In this study, the proportion of children who receiving the BCG vaccine (95%) was higher than those receiving the first dose of the polio vaccine (79%). This finding indicates there are still missed opportunities and highlight the challenge of introducing early polio vaccine which should be given within 24 h after birth.
In our study, there was a decline in coverage of immunization from BCG at birth (94.7%) to measles (82.1%). Overall, the dropout rate between BCG vaccine and measles vaccine was around 11%.
Our findings corroborate with those in Nigeria, Guinea, and Uganda [
18‐
20]. A plausible reason to explain reduction in the proportion of full vaccination coverage when children get older compared to vaccines received after birth may be due to logistical problems but also the fact that some mothers may not understand the routine immunization schedule [
6] or may not choose to come back after adverse events following the first contact with the immunization system. In a study in West Africa, factors determining completion of the DTP3/Oral polio vaccine included past experience with vaccination services (short waiting time, not having been turned away or not knowing a child with post vaccine adverse events). The high dropout rate means that difficulties still exist in immunization program utilization specifically the follow-up of children throughout the immunization schedule [
6].
Our study revealed that 77.14% of children were fully immunized according to mothers recall while only 37.5% were classified as fully immunized when only the vaccination card was considered. Similar findings in the differences between the two methods have been previously described in Nigeria and Ethiopia [
13,
20]. In addition to recall bias, this difference may be the result of mothers without a health card to tend to provide answers that will be viewed favorably by the interviewers, or social desirability bias. Thus, this situation may lead to overestimation of doses really received by the children.
Our results indicate that out of the four main geographic areas, the eastern regions had the lowest rate of immunization coverage and there is significant regional difference as children from southern regions had the highest rates. This difference may be due to differences in the uptake of immunization services based on cultural beliefs or differences in the quantity and/or the quality of health care services between the administrative regions [
7,
21]. This may also be explained by, vaccine procurement, supply, cold-chain, or differences in other logistics issues between regions [
22,
23].
In this study, children born from mothers who attended antenatal care during pregnancy or who gave birth at the health facility were more likely to be fully vaccinated. Similar findings were seen on other studies in LMICs and sub-Saharan African countries [
6,
13‐
15]. This may be explained by the fact that in Senegal local health centers are the backbone of the primary health care approach and offer a range of preventive and curative services including immunization programs, which have been strengthened at the district level between 2001 and 2005 following WHO recommendations. An intervention called “The Reaching Every District strategy” [
15,
22,
24] has been used to strengthened the immunization system and support low performance health districts. With the adoption of this strategy, public health facility managers were encouraged to implement the principle of good immunization practices. This strategy also included the identification, and resolution of local problems, organization of regular outreach in vaccine delivery services and community participation in raising vaccine coverage. Another strategy adopted at the district level in Senegal was the integration of childhood immunization into all aspects of child health care delivery.
The capacity to achieve equity is a key component of national immunization programmes [
21]. In this study, we analyzed equity in immunization coverage with regard to areas of residence (urban versus rural) and the household wealth index (full immunization coverage by wealth quintile). Our multivariate analyses results showed no significant associations between full immunization and areas of residence or household wealth index. These findings were not confirmed by results seen in other African and other LMI countries [
4,
12,
13,
16,
18,
25]. In a study in Ethiopia, Lakew et al. [
13] showed that children born from mothers of higher wealth index were 40% more likely to have received full vaccination status compared with children from women of poor wealth index group. However, in their study, the wealth quintile was categorized only into three groups (poor, middle and rich) and the percent coverage among children in the lowest quintile group was very low compared to our study (17.5% vs 61.9%). Similarly, Lynch et al. demonstrated that higher economic status was associated with better health [
25]. However, in their study they used a more complex definition of health including quality of life, life expectancy, and specific measure such as causes of death [
25].
Our study focused on nine vaccines available at the time of the survey used for theses analyses. However, in 2013 and 2014, Senegal launched a large-scale introduction of the pneumococcal vaccine and the rotavirus vaccines. Additionally, a human papilloma virus (HPV) vaccine to prevent cervical cancer among adolescent girls aged 9–13 years old is expected to be added to the vaccines offered in 2017. With the introduction of these new antigens into the routine immunization schedule, the number of vaccines offered by the national EPI through the public health infrastructures is expected to rise. However, there is a risk that the introduction of these new vaccines may negatively impact the delivery of traditional vaccines such as BCG vaccine, pentavalent, measles and polio vaccine [
26]. Therefore, current strategies should focus on planning and strengthening the health system to make sure the rates of immunization coverage is not affected by the addition of new vaccines.
Limitations of the study
Our study has some limitations. First, information on child’s immunization was collected from either the health card or the mother’s recall of vaccinations as recommended by the World Health Organization. However, because of potential shame and social stigma, mothers of children who don’t have the vaccination recorded on the health card may be more tempted to report a vaccination for their children introducing a potential subject bias. Consequently, the level of immunization coverage may be lower than the prevalence reported in this study. Second, information on immunization and certain sociodemographic characteristics was collected at the same time, therefore it may be difficult to establish a causal relationship between these characteristics and the child immunization status. Third, in this study, based on the birth history, only living children were included, therefore the generalizability to all children, living and deceased, remains unclear.
Acknowledgments
We thank Christopher S. Murrill who provided useful comments during the preparation of this manuscript. We also thank Macro International and the DHS programme for granting permission to use the Demographic and Health Survey for this research.