Individual and socioeconomic factors associated with childhood immunization coverage in Nigeria

Introduction Immunization is the world’s most successful and cost-effective public health intervention as it prevents over 2 million deaths annually. However, over 2 million deaths still occur yearly from Vaccine preventable diseases, the majority of which occur in sub-Saharan Africa. Nigeria is a major contributor of global childhood deaths from VPDs. Till date, Nigeria still has wild polio virus in circulation. The objective of this study was to identify the individual and socioeconomic factors associated with immunization coverage in Nigeria through a secondary dataset analysis of Nigeria Demographic and Health Survey (NDHS), 2013. Methods A quantitative analysis of the 2013 NDHS dataset was performed. Ethical approvals were obtained from Walden University IRB and the National Health Research Ethics Committee of Nigeria. The dataset was downloaded, validated for completeness and analyzed using univariate, bivariate and multivariate statistics. Results Of 27,571 children aged 0 to 59 months, 22.1% had full vaccination, and 29% never received any vaccination. Immunization coverage was significantly associated with childbirth order, delivery place, child number, and presence or absence of a child health card. Maternal age, geographical location, education, religion, literacy, wealth index, marital status, and occupation were significantly associated with immunization coverage. Paternal education, occupation, and age were also significantly associated with coverage. Respondent's age, educational attainment and wealth index remained significantly related to immunization coverage at 95% confidence interval in multivariate analysis. Conclusion The study highlights child, parental and socioeconomic barriers to successful immunization programs in Nigeria. These findings need urgent attention, given the re-emergence of wild poliovirus in Nigeria. An effective, efficient, sustainable, accessible, and acceptable immunization program for children should be designed, developed and undertaken in Nigeria with adequate strategies put in place to implement them.


Introduction
Immunization remains one of the most successful and cost-effective public health interventions worldwide, preventing (and/or eradicating) several serious childhood diseases [1]. Although existing immunization programs prevent over 2 to 3 million deaths annually that could have resulted from vaccine preventable diseases (VPDs), 19.4 million children missed out on basic vaccination globally in 2015 [2]. This results in an estimated 2.7 million child deaths annually from VPDs, the majority of which occur in sub-Saharan Africa, which accounts for the increasing under-5 years-old mortality rate in sub-Saharan Africa and South Asia, as these two regions accounted for 82% of under-5 years-old deaths in 2011 [3].
The expanded program on immunization (EPI) was launched by the WHO in 1974 and has averted over 15.6 million deaths since 2000 through measles immunization, elimination of maternal and neonatal tetanus from 35 out of 59 high-risk countries, and the dramatic reduction of the prevalence of polio globally [4]. Nigeria  A score of 4 (BCG = 1, DPT3 = 1, OPV3 = 1, and Measles = 1) meant complete immunization while anything less than this was seen as incomplete immunization. DPT3, BCG, OPV3 and measles were combined to compute a new variable named 'Completed Immunization'. Children who had none were classified as having not received vaccination-even if they had OPV0, 1 or 2; or DPT 1 and 2.
This was further recoded to have children who had received the four vaccines as only those who completed vaccination. The key independent variables in this study were individual and socioeconomic factors of the participants in the NDHS 2013 study.
These include age, marital status, highest education level, husband's/partner's education attainment, literacy, wealth index, the respondent having worked in the last 12 months, and the respondent's occupation [11]. Child-related independent variables were child birth order and child gender. These variables were dichotomized for logistic regression analysis. For instance, parental age was re-classified into less than 30 years and above 30 years, In the ''received vaccination'' group, all those who stated they did not have the vaccination were grouped along with those responded ''don't know'' with the assumption that mothers were unlikely to ever forget immunizing their children. Furthermore, all those who said their children were vaccinated were grouped together whether and multivariate (logistic regression) analyses were performed to identify associations and measure levels of significance between independent and dependent variables [12]. We calculated the correlation coefficient (r), alpha values and confidence intervals [12]. Finally, we performed multiple logistic and linear regression analyses to reduce statistical errors [13].

Results
A total of 31,482 persons who responded to the survey had children within the age range of 0 to 5 years, with an average age of 29.46 ± 7.0 years, and a modal age range of 30 years. A total of 31,482 persons who responded to the survey had children within the age of 0 to 5 years, with an average age of 29.46 ± 7.0 years, and a modal age of 30 years.

Univariate analysis:
The sociodemographic details are as depicted in Table 1. All were or had ever been married, about one-third (10352, 31.9%) resided in urban regions of their respective states, 17.7% (5596) started primary (6.2) and secondary (11.5%), but did not complete their education, while only 19% (5991) had 6 or more children in their households. Among the husbands/partners, 85% (23,432) were 30 years or older, 65.8% (18.138) were either professionals or involved in skilled manual work, and 39.9% (10,991) were unable to read as shown in Table 2 Bivariate and multivariate analysis: In bivariate analysis, respondents' age, place of residence, religion, education, literacy, wealth index, occupation, and marital status were all significantly related to immunization coverage and completion of immunization, as shown in Table 4, Table 5. Similarly, the respondents' partner/husbands age, occupation and education were all significantly related to immunization coverage. While child birth order, the number in the family, the delivery place, and the presence or absence of a child health card were all significantly related to immunization coverage, the sex of the child was not. All the above factors were therefore significantly related to immunization coverage rates in 2013 in Nigeria. Marital state of respondents and sex of the child were not significant in binary logistic analysis. Correlation coefficients were computed among the various independent variables with the dependent variables.
Correlations coefficient with control for Type 1 error using the Bonferroni correction showed that high literacy, better wealth index, and residing in the southern part of Nigeria were significantly related to improved vaccination rate as shown in Table 6. Similarly, only high husband/partner's literacy; the child's place of delivery, the presence of a health card, and the number of children in the family significantly related to improved vaccination rate from correlational studies. Using a five level concept for the complete vaccination process, correlation between the complete immunization and region (r=0.38); educational attainment (r=0.47); religion (r=0.39); literacy (r=0.46); and wealth index (r=0.42); displayed statistical significance (p.001). We went on to perform linear (bivariate and multivariate) regression analysis to evaluate the completion of immunization from respondents, husband/partners' and child factors using a random-effects model [11]. The 95% confidence interval for the slope shows that the respondent, husband/partner and child overall relationship was significantly related to the immunization coverage. However, the accuracy in predicting the immunization coverage was moderate, as can be seen in Table 7. Finally, we undertook a multiple regression analysis to evaluate how well the factors of interest predicted immunization coverage in children. The linear combination of maternal, paternal and child variables were significantly related to immunization coverage, maternal R2 = 0.3; husband/partner R2 = 0.19; and child R2 = 0.39. The sample multiple correlation coefficient was 0.53 (maternal), 0.51 (husband/partner) and 0.37 (child). The respondents' age, educational attainment and wealth index at 95% confidence interval showed a significant relationship between these variables and immunization coverage of children Table 6, Table 7.

Discussion
In this Nigerian study, less than 23% of targetable children received complete immunization and close to one third of the children did not receive any vaccination at all. This is similar to the findings of Obiajunwa and Olaogun in 2013 in South-Western Nigeria where they recorded 26.5% coverage in a region which was expected to have very high immunization coverage [14]. In Ethiopia, Lakew et al. (2015) found that there was just 24.3 % full immunization coverage [15]. It is also similar to the WHO's assertion in 2015 that  [14]. Among the nonvaccinated, more than 48% did not receive BCG vaccination, and over 50% of the children did not receive DPT 1, 2, and 3. The 55% of children who did not receive the 'Polio 0' vaccine may be a reflection of the high level of home delivery in Nigeria, estimated to be 40% to 45% [21]. household, and interaction between literacy and wealth were found to be significantly associated with complete vaccination [22].
However, the sex of the child was found not to be significant in determining immunization coverage in Nigeria (p > 0.05). Who Page number not for citation purposes 5 attended to the birth of a child (similar to delivery place) had previously been found to affect immunization coverage in Lao People´s Democratic Republic [23]. A similar finding was also documented by Fatiregun and Okoro in 2012 in a previous Nigerian study [24]. In another study in Ethiopia, researchers discovered that having a vaccination card improved the chances of immunization coverage [15]. However, how immunization card presence affects coverage is unknown and required further qualitative or mixed studies.

Maternal factors:
In previous studies, maternal factors have been found to impact childhood immunization coverage [14,23,25]. In this study, statistical analysis revealed that maternal age, region, were studied in this work, maternal factors were clearly shown to affect commencement, continuation, and completion of the required number of immunizations as maternal age, education, and occupation were still statistically significant factors affecting immunization coverage in multivariate analysis [23,25]. Moreover, geographical location (i.e. region) was previously documented to influence immunization coverage by Doctor et al. (2011) in northern Nigeria, with people living in urban areas having usually higher coverage rate [26]. This may be a result of better access, a good transportation system, higher rates of literacy, and a better wealth index. This was not, however, studied in this current work as the dataset analyzed did not differentiate respondents based on urban or rural locations. The influence of religion as a factor was also documented by Ophori et al. (2014) [27]. Furthermore, the findings of Lakew et al. (2015) in Ethiopia are similar to this as they discovered that full immunization coverage was commoner among women in rich wealth index groups [15]. factors hindering immunization coverage are preventable with the right political will, proper funding and social mobilization. We should institutionalize routine immunization to save Nigerian children from avoidable VPDs, and untimely deaths. We call on all stakeholders to safeguard the health of Nigerian children. Immunization should be made compulsory for all children. Parents should be supported to access these services. Health insurance should be provided to reduce out-of-pocket expenditure and community support should be galvanized to ensure that every child is fully immunized. Finally, mentors should be developed for families with high birth order to ensure that no child fails to receive vaccination. The re-emergence of WPV in Nigeria should provide the motivation needed to make the necessary changes in the healthcare industry.

What is known about this topic
 Immunization is the most effective and efficient public health intervention known to man;  Although, 2 to 3 million children have been saved by immunization in recent years, over 2,000,000 children still die yearly from vaccine-preventable diseases;  Nigeria remains a major contributor to global VPD deaths, habitat for polio virus and a rate determining step in the fight to eradicate polio from the world.

What this study adds
 Nigeria immunization coverage rate is low -less than 25% completion rate. Thus, several avoidable childhood deaths occur from vaccine-preventable diseases (VPD);  This study identified statistically significant child, maternal and paternal factors that hinder the achievement of projected immunization coverage rates in Nigeria;  These factors must be addressed for Nigeria to make meaningful progress towards the elimination of vaccine preventable diseases in the country.

Competing interests
The authors declare no competing interest.

Authors' contributions
The current work forms part of OOO's PhD dissertation. VK was the Chair of the Dissertation Committee, while AA was a member of the committee. OOO conceptualized, organized, and wrote the initial