Vaccines have proven invaluable in fighting several childhood illnesses, including poliomyelitis, measles, rubella, and tetanus. In 2022, the World Health Organization (WHO) estimated global diphtheria, pertussis, and tetanus (DPT) coverage among children under 12 months was 84%, ranging from 72% in the African region to 93% in the Western Pacific [1]. Ninety percent of mortality in children under five in developing countries is caused by pneumonia, malaria, diarrhea, measles, and neonatal causes such as prematurity, asphyxia, and neonatal sepsis [2]. Despite the substantial progress that continues to be made, many children, particularly those in less developed countries, remain at risk of vaccine-preventable diseases, which makes achieving high and equitable coverage a challenge in unequal countries like Namibia [1, 3].

The immunization program in Namibia (Supplementary Table S1) is implemented by the Ministry of Health and Social Services through the Expanded Program on Immunization (EPI), which was established nationwide in 1990 [4]. The EPI program in Namibia follows WHO guidelines for children’s vaccination. To be considered fully vaccinated, a child should receive a dose of the Bacillus Calmette-Guerin (BCG) vaccine against tuberculosis at birth and no later than a year thereafter; three doses of DPT for the prevention of diphtheria, pertussis (whooping cough), and tetanus at intervals of four weeks; at least three doses of polio vaccine; and vaccination against measles and rubella(M&R), at nine months and 15 months, respectively [1, 4]. BCG is given at birth or soon thereafter, while DPT and polio vaccinations should be administered at approximately 4, 8, and 12 weeks of age, respectively; however, recently, a dose of polio at birth has been added to the schedule. The measles and rubella vaccines should be given at or soon after reaching nine months [1]. According to information from both vaccination records and maternal recall, only 65% of Namibian children aged 12–23 months can be considered fully immunized [4]. Although the coverage levels for BCG and the first doses of the pentavalent including DPT, Hepatitis B(Hep), Haemophilus influenzae type b(Hib) vaccine, and polio vaccine exceed 90%, the proportion of children who go on to receive the third dose of these vaccines falls to 79% for DPT, Hep, Hib and 77% for polio [1, 4]. Eighty percent of children aged 12–23 months have received the measles vaccine. Five percent of children have not received any vaccinations at all, according to data [1, 4, 5].

Expanded Program of Immunization has contributed to improvements in coverage; however, the proportion of children completing the recommended vaccination schedule has not increased as anticipated [6]. The utilization of vaccination services and completion of the recommended schedule are determined by numerous factors, and vaccination coverage rates vary greatly across countries and regions. Several studies state that the birth order of the child, mothers’ educational status, family size, distance to a health facility, mothers’ knowledge score, place of delivery, antenatal care(ANC) follow-up, and tetanus toxoid immunization were found to be significantly associated with children’s full immunization status [1, 2, 6, 7]. Other studies indicate that religious affiliation and exposure to mass media are predictors of poor immunization coverage. However, the relationship of these factors in predicting full immunization has not always been consistent across study areas [8, 9].

Opuwo District is the capital town of the Kunene region, situated in northwestern Namibia. It is vast, dry, mountainous, remote, and sparsely populated, with very poor infrastructure and geographical barriers that pose significant challenges for health service delivery. The region is also prone to outbreaks of diseases like Malaria, Measles, and Schistosomiasis, especially among residents living along the Kunene River. Vaccine-preventable diseases such as Pneumonia and Diarrhea remain the leading causes of morbidity in the Opuwo District, particularly among the nomadic communities in this area.

Our study aims to identify the factors contributing to children’s immunization rates in a less developed area like Opuwo District in Namibia, shedding light on how to improve healthcare for children in underdeveloped regions. This could help develop strategies and interventions to increase vaccination rates among children in these areas. It may also assist in implementing policies to reduce vaccine-preventable diseases in children.

The researcher used a cross-sectional, descriptive quantitative study to determine the vaccination status among children aged 1 month to 24 months. The Namibia Health Ministry's electronic system (DHIS) was used to generate data for analysis to determine vaccine coverage among the districts. A quantitative approach allows for the identification of potential contributing factors [10].

Survey questionnaire was designed refer to previous studies [7, 8], details in in Supplementary Materials S2. Questionnaire was first tested in five health facilities, and adjustments were made according to the feedback received before starting the main study. Ethical clearance was obtained from the Southern Medical University International Students Postgraduate Studies Committee. The researcher sought permission from the Ministry of Health as well as from the Kunene Regional Director. Furthermore, consent was obtained from the person in charge of the selected health facilities, and written informed consent was obtained from the participants after the purpose and objectives of the study were explained to them prior to the issuance of the questionnaire (Supplementary Materials S1). Confidentiality and anonymity were maintained, as no names were entered on the questionnaires, and participants were informed that they could withdraw from the study at any stage should they feel the need to, without any punishment or harm.

Opuwo District has an estimated total population of 2,535 children under 1 year of age as of 2020, of which 1,879 are targeted to be fully immunized for the financial year. The target population of the study was parents and caretakers of children under the age of 24 months who visited health care services during the data collection period.

The research employed combined sampling methods: simple random sampling and systematic sampling to determine the sample size. The sample size was calculated using Statcalc in Epi Info 7 and SPSS, with the population size set at 2,535, expected frequency at 10%, cluster sample as 131, and expected confidence interval of 95%. The cluster sample was also considered as 94 with an expected confidence interval of 90%.

A fully immunized child within 24 months of age is defined as a child who has received one dose of BCG and Hep, three doses of pentavalent, Pneumococcus (PCV), Oral polio vaccine (OPV), two doses of rotavirus, and one dose of measles at the appropriate age. Immunization coverage calculation is based on the defined period, antigens, and target population.

The researcher gathered data through the assessment of the children’s health care passports, immunization cohort registers in selected health facilities, as well as the DHIS data for the district, including the number of children immunized by vaccine (from April 2019 to March 2020) and population information to calculate the coverage of DHIS data. The researcher also distributed written online questionnaires to the parents or caretakers of the children. The questionnaire was designed in sections according to the study objectives and consisted of both close-ended and open-ended questions.

Data was entered, cleaned, coded, and edited for inconsistencies, and data analysis was performed using IBM SPSS version 25. The data were analyzed in SPSS using one-way ANOVA and univariate analysis. The data were analyzed quantitatively using descriptive statistical methods and were presented through the use of tables, charts, and graphs.

Six thousand seven hundred seventy-four population records from the Kunene Region and 4,976 records from the Opuwo District were collected from the DHIS system for immunization and calculations. Sixteen health facilities were employed for the survey study. The response rate of the health facilities was 87.5%, with a rejection rate of 12.5% (2 facilities). A total of 117 parents/caretakers of children under 24 months attending or seeking healthcare services at 14 health facilities were calculated per clinic population. The sample size per facility was calculated using random sampling; however, not all clinics reached the sample size. Ultimately, we received 116 valid questionnaire results for analysis.

The majority of the participants accompanying children to the surveyed health facilities were between the ages of 20 and 34 (60.7%). Participants aged 35 to 44 made up 25%, while those aged 55 years and above were the least represented at 3%. Additionally, 94% of the participants (those accompanying children to the facility) were female, while only 6% (n = 7) were male.

Children under eight months represented half of the population (n = 63; 54%). Children aged 9 to 14 months comprised 26% (n = 30), and children aged 15 to 24 months represented 20% (n = 23). The proportion of male children was similar to that of female children, with males comprising 51.3% (n = 60) and females 48.7% (n = 57).

Vaccine coverage of Opuwo District and Kunene region through DHIS data mostly reach the 80% percent coverage among the antigens (Fig. 1 and Table 1). Only antigens of PCV, IPV and second dose of Measles and Rubella not meet the level. According to our survey results, 49% of the children have received the recommended antigens by the age of 12 months, which is similar to DHIS data (47%). However, our data show lower coverage compared to the DHIS data in general, especially for records of second and third dose (Fig. 1 and Table 1).

Child immunization coverage in the Kunene Region and Opuwo District from April 2019 to March 2020, comparing DHIS data with the survey data. Abbreviations: OPV,oral polio vaccine; Pentavalent, vaccine that prevents five diseases, including diphtheria, pertussis, tetanus, hepatitis B, and Haemophilus influenzae type b; PCV, pneumococcal vaccine; IPV, inactivated polio vaccine; M&R, measles and rubella vaccine

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According to our survey data, most children received the first doses of OPV (84%), Pentavalent (DPT, HepB, Hib) dose 1 (73%), PCV dose 1 (72%), and Rotavirus (72%) compared to the second and/or third doses of the same antigens. However, the number of children who received second doses declined; for instance, only 60% of children received the second dose of OPV, compared to DHIS data (101%). The Pentavalent vaccine showed a drop to 60% of children receiving the second dose, compared to DHIS data (100%). PCV and Rotavirus also showed declines, with 60% and 59% of children receiving the second dose, respectively (Table 1).

98 (84%) of children have received the BCG birth dose, which is given immediately after birth. Seven children (6%) received the BCG dose at a later stage after birth but before the age of one, while 9 children (7.8%) were not immunized against BCG during the data collection period. Among the participants, 41 children had received the IPV vaccine at the recommended age, 3 had received it later, and 10 had not received the dose at all. At least 34 (29%) and 14 (12%) of the 116 children had received the measles and rubella vaccines at 9 months and 15 months, respectively, while 8 and 6 children had not received any measles or rubella vaccines at either 9 or 15 months (Tables 1 and 2).

To explore the demographic factors associated with children's vaccination status, we analyzed the collected data using SPSS, employing one-way ANOVA and univariate analysis. We did not observe correlations between factors such as sex (P = 0.094), living in a rural/urban area (P = 0.080), and ethnicity (P = 0.695) and the immunization status. Significant differences were, however, observed in children born in hospitals < 0.001), birth order (p = 0.017) as well as in Distance from the health facility (univariate analysis; P = 0.020). Versus those born at home (P < 0.001), birth order (P = 0.017), and distance from the health facility (univariate analysis; P = 0.020) (Table 3).

According to our survey data, 77 children (65.8%) were born in a hospital, while 40 children (34.2%) were born at home. Fifty-two children (45.2%) born in a hospital were fully immunized, whereas only five children (4.3%) born at home were fully immunized. The proportion of children with partial immunization was 20% (n = 23) for those born in hospitals and 30.4% (n = 35) for those born at home. A significant difference in immunization status was observed between children born in health facilities and those born at home (P < 0.001) (Table 3).

Birth order is also considered a factor influencing immunization status. We examined first, second, third, and fourth or higher birth orders in our study. The results showed that 10.4% (n = 12) of first-born, 19.1% (n = 22) of second-born, 9.6% (n = 11) of third-born, and 10.4% (n = 12) of fourth or higher born had completed the immunization schedule. Meanwhile, 15.7% (n = 18) of first-born, 9.6% (n = 11) of second-born, 7% (n = 8) of third-born, and 18.3% (n = 21) of fourth or higher born had missed one or more vaccine doses. We found that second and third childbirth order children were more likely to be immunized against all recommended antigens compared to others (P = 0.017) (Table 3).

Distance from the health facility is believed to be one of the factors associated with immunization status. Most participants (n = 48; 41%) reside in areas less than 10 km from the health facility, 30.8% (n = 36) within 30 km, 21.4% (n = 25) within 60 km, and 6.8% (n = 8) residing more than 60 km from the health facility. The number of fully immunized children decreased as the distance increased: 27% (n = 31) of children living within 10 km were fully immunized, 14% (n = 16) of those within 30 km, 7% (n = 8) of those within 60 km, and 1.7% (n = 2) of those beyond 60 km. At least 14% (n = 16) of children residing within 10 km were partially immunized, 17.4% (n = 20) for those residing within 30 km, while 15% (n = 17) and 4.3% (n = 5) were for those residing within 60 km and beyond 60 km, respectively. Univariate analysis revealed that children residing within 10 km of health facilities were more likely to be fully immunized than those living farther away (P = 0.020) (Table 3).

According to our survey data, 40.3% of maternal/caretakers (n = 46) had no education, 20% (n = 23) had a primary education, 32.3% (n = 37) attended secondary school, and 7.7% (n = 9) had tertiary education. Among the participants, those who never attended school were unemployed (100%, n = 47). Those with primary education were mostly unemployed (91.7%, n = 22) or self-employed (8.3%, n = 2), while those with secondary education were 81.1% unemployed (n = 30), and 5.4% (n = 2) had formal jobs; the rest were students (13.5%, n = 5). Those with tertiary education were mostly employed (77.8%, n = 7), while a few were unemployed (11.1%, n = 1) or still students (11.1%, n = 1) (Table 4).

Children of caretakers with no educational background had the highest rates of incomplete immunization (31.3%, n = 36) and missed one or more vaccines. Those with tertiary education reported that eight out of nine children (88.89%) had a complete vaccine schedule, while those with primary and secondary education had only 13% (n = 15) and 21% (n = 24) fully immunized, respectively. Statistical analysis found that children of parents or guardians with tertiary or secondary education were more likely to be completely immunized than those of parents with no education (P < 0.001). In addition, our results showed that there was a significant relationship between occupation and immunization status (P = 0.001) (Table 4).

The information enhances knowledge and understanding of the importance of vaccination for children; thus, data were collected to analyze the relationship between the source of information and immunization status. According to our survey data, among multiple respondents, health care workers (including nurses, doctors, and health assistants) were reported as the primary source of information (n = 140), followed by friends/family and clinic committees (n = 13), radio and other media platforms (n = 10), while church or traditional leaders received the least attention (n = 0). Among those who reported health care workers as their source of information, 60 (42%) children were fully immunized, and 70 (44.6%) were partially immunized. Among respondents who identified family/friends or clinic committees as their source of information, only 5 (3.2%) were fully immunized. Those who reported radio and other media platforms as their source had an equal number of fully and partially immunized children, with 5 (3.2%) each. There was no significant difference observed between the source of information and immunization status (P = 0.056) (Table 5).

In our survey study, 89.5% (n = 103) of mothers attended ANC, while 9.5% (n = 11) did not attend, and 1% (n = 1) were unsure. Of the children whose mothers attended ANC, 47.8% (n = 55) were fully immunized, while 41.7% (n = 48) were partially immunized. There was a statistically significant difference between immunization status and mothers who attended antenatal care (P = 0.036).

Most respondents (32.4%, n = 36) indicated that they lived far from the hospital. Additionally, 31 (27.9%) reported not having money for transport to the health facility, 16 (14.4%) were unaware that their child/children were due for immunization, and 9 (8.1%) claimed that their child was sick and therefore not fit for immunization. Others stated that their child was still too young for certain doses or that they did not have time to go to the health facility due to being busy (4, 3.6%). Three (2.7%) did not find certain vaccines at the health facility, while 8 (7.2%) had other reasons. This result suggests that many people live far from hospitals and have limited financial resources, making it challenging to access health facilities, even though health services are free in Namibia.

Furthermore, this result indicates a lack of insightful knowledge and awareness. For instance, 14.4% were not aware of whether the immunization was due. Among the other 7.2%, some responded that they had no reason or that they lived alone, while 3.6% claimed they were too busy to go to the health facility. This indicates little to no adequate knowledge pertaining to immunization and its significance.

This study was conducted to analyze and assess vaccine coverage, vaccine status, and associated factors in the Opuwo district of Namibia. Our results showed that only 48.7% of the children have been fully immunized. Factors such as educational level, parental occupation, child’s place of birth, ANC attendance, knowledge, and birth order were significantly associated with the immunization status of children. These results can provide valuable information for policymakers to develop strategies to improve child care. In general, our survey results reveal lower vaccine coverage compared to DHIS data, possibly due to the low coverage of nomadic populations, indicating a need for vaccine coverage monitoring and further investigation in this area.

The data from our survey indicated that many children in the Opuwo district miss the second and third doses, possibly because they do not return to the health facility or because the healthcare workers do not record the vaccines administered in the health passport. Additionally, the country has faced a shortage of certain vaccine antigens for several months. This result is similar to a study in Africa which found an estimated relative Pentavalent dropout of 10% or lower in 2016 in northern Africa, Namibia, and eastern Africa. More than 90% of children who received the first dose of DPT went on to complete the three-dose series [13]. Other studies have also reported similar findings [14, 15].

A large proportion of children received vaccines against several antigens at the recommended age compared to those who received them later or did not receive them at all. The results align with those of a study conducted in Ethiopia [11]. Conversely, this study shows lower rates compared to studies conducted in Istanbul [12] and Mali [13], where the proportion of fully immunized children was 84.5% and 59.9%, respectively. These results may be attributed to the geographical characteristics of the district and the literacy level, particularly due to the nomadic inhabitants who have less or no knowledge about child immunization, as well as cultural beliefs and reluctance to adapt to the modern world.

However, there was an alarming number of missing values/records related to pentavalent and M&R vaccination. Although 54% (63) of the children were under the age of 8 months and did not qualify for measles vaccination, 10% of those above 9 months did not receive the measles vaccine. The number of children receiving the second and third doses declined by more than 10%. This may indicate that there are children who received the first dose of vaccines but did not return for the second and third doses in the same series of immunization. At least 84% of children had received the BCG vaccine; however, the study found that 1 in 12 children in the Opuwo district was not immunized with BCG during the period of data collection. These results are consistent with a study conducted in northern Nigeria, which found that only 37.3% of children had received the BCG vaccine [14]. On the other hand, there was a significant difference in vaccine coverage data calculated from DHIS and our survey, possibly due to an underestimation of the nomadic populations or data collection bias.

In this study, there was no significant difference related to sex and complete vaccine status. The result is similar to that of a WHO partner, indicating that males and females had the same likelihood of not being vaccinated. Another study conducted in India also found no difference in sex and completion of vaccination [15]. However, in other studies, some countries showed females being more likely to be unvaccinated, including India in 2012–2013 (Male OR = 1.17, CI = 1.01–1.13) [16], Yemen in 2010 (Male 72.1% VS Female 66.8%) [17], and in developing countries like Zambia Ethiopia and China, but change over time [18]. These results suggest that associated factors may change over time due to social development and improvements in education.

Furthermore, this study found that children of parents or guardians with tertiary or secondary education were more likely to be completely immunized than those whose parents had no education. This is similar to a study conducted in Kenya, where women with primary, secondary, and university education were more likely to have their children immunized [19]. Similar findings have been reported in other studies [20, 21]. In addition, those with formal employment generally have better financial means compared to the unemployed; therefore, this may affect their children's immunization. Although child immunization is offered for free in public health facilities, those without formal jobs may struggle with transportation costs. This result is consistent with other studies [22, 23]. The knowledge and economic level of parents are significantly closely related to children’s immunization status. Stock shortages for certain vaccines also affect the immunization status of children, and some may not return to the health facilities when stock arrives for missed doses due to factors such as lack of funds or limited information.

More attention needs to be paid to other factors associated with children's immunization status. Children born in hospitals had higher rates of complete vaccination than those born at home, a finding that has also been reported in studies conducted in Ethiopia [24], Uganda [25], and Sub-Saharan Africa [26]. Surprisingly, this study found that children who are second or third in childbirth order are more likely to be immunized against all recommended antigens than others. This result is similar to findings from other studies [27]. On the other hand, children residing within 10 km of health facilities were more likely to be fully immunized than those living farther away, as found in our study, as well as in Burkina Faso [28] and in Ethiopia [2, 7, 8, 11, 23, 24].

In summary, this study revealed that more needs to be done to improve vaccine coverage and to ensure that every child in this district is reached and fully immunized. To enhance immunization coverage and status in the district, there is a need for community education, improved outreach healthcare services, and well-developed immunization programs, as well as monitoring of nomadic populations and second and third dose immunizations to ensure all children are reached and fully immunized.

ANC:

Antenatal care

BCG:

Bacillus Calmette-Guerin

DHIS:

Namibia Health Ministry's electronic system

DPT:

Diphtheria, pertussis, and tetanus

EPI:

Expanded Program on Immunization

Hep:

Hepatitis B

Hib:

Haemophilus influenzae type b

IPV:

Inactivated polio vaccine

M&R:

Measles and rubella vaccine

OPV:

Oral polio vaccine

OR:

Odds ratio

PCV:

Pneumococcus vaccine

WHO:

World Health Organization

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Author notes

L.S. M. A. collected the raw data and designed the study. L. S. M. A., and J. O. prepared the figures and tables, and wrote the original manuscript text. J. O. and Q. Z. revised and checked the data and results. C. W., W. Z., Z. F., and Q. Z. reviewed and revised the manuscript. All authors reviewed the final manuscript.

Correspondence to Wei Zhao, Zhixin Fang or Qiwei Zhang.

This study adhered to the Declaration of Helsinki and was approved by the Ethics Committees of Southern Medical University. All participants provided informed written consent for all study procedures and for the use of their data for scientific evaluation and publication.

Not applicable.

The authors declare no competing interests.

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