This was a descriptive cross-sectional study of the vaccination status of children aged 0 to 59 months attending the Pediatric Department of CHU-YO. Data was collected from July 15, 2023, to November 15, 2023.

Our study included all children under 59 months of age admitted to the Pediatric Department of CHU-YO during the study period. All children with an available and usable vaccination record were included. Children for whom vaccination was contraindicated were not included. A structured questionnaire was used to collect information from consenting mothers/caregivers and health workers.

Data were collected through interviews with parents or guardians using a questionnaire and by reviewing each child’s vaccination record at the outpatient clinic and in the various inpatient units of the Pediatric Department of the CHU-YO. A self-administered questionnaire was given to the health workers present.

The variables collected were socioeconomic and demographic data, children’s personal and family history, vaccination status, missed opportunities for vaccination, and the reasons for MOV. The vaccination schedule used was that of the Expanded Program on Immunization in force in Burkina Faso in 2023. A child was considered up-to-date with their vaccines if they had received all the vaccines they were supposed to receive for their age. A child was considered correctly vaccinated if they had been vaccinated according to the EPI and non-EPI vaccine schedules [13] . A child was considered completely vaccinated if they had received all EPI and non-EPI vaccines. The Expanded Program on Immunization (EPI) targeted 13 diseases in children from 0 to 15 months, including vaccines at birth (tuberculosis, polio, hepatitis B); at 2 months (diphtheria, tetanus, pertussis, hepatitis B, Haemophilus influenzae b (Penta 1), poliomyelitis, rotavirus diarrhea, pneumococcal infection); at 3 months (Penta 2, poliomyelitis, rotavirus diarrhea); at 4 months (Penta 3, poliomyelitis, rotavirus diarrhea, pneumococcal infection); at 9 months (measles, rubella, yellow fever poliomyelitis, and pneumococcal infection); and at 15 months (measles, rubella, and serotype A meningitis) . Non-EPI vaccines for children under 59 months of age included vaccines against meningitis (serotype ACYW135) between 18 and 24 months, typhoid fever from 2 years of age, Penta 4, pneumococcal infection, rotavirus diarrhea, poliomyelitis between 16 and 18 months, and the measles, mumps, and rubella (MMR) vaccine from 15 months of age [13] .

The collected data were entered into a microcomputer and analyzed using STATA and SPSS software. We described the socio-demographics and clinical characteristics of study participants. The proportion of MOV and its 95% confidence interval was estimated. Quantitative data were described using means and standard deviations. Categorial data were described with proportions.

For our study, we received the agreement of the general management of the CHU-YO for data collection, as well as the approval of the Ethics Committee for Health Research N˚2023-07-185. Data were collected after explaining the study, obtaining signed informed consent from parents, and filling out anonymous forms. Data were processed anonymously to ensure the confidentiality of all patients.

The study involved 420 children and their caregivers. Of these, 36% (150/420) of the children were not hospitalized. The average age of the children was 15.84 months with a standard deviation of 16.61 months, and an age range from 0 to 59 months. Males accounted for 59%. The majority of children (98%, 411/420) were born in a health center. There were 74/85 health workers, including 12 doctors and 62 paramedics. Females represented 60 cases, or 81.08%; 65, or 87.83%, had more than three years of experience. Table 1 shows the characteristics of children and their parents.

Missed opportunities for EPI vaccination were observed in 156 children (37.14%, 95% Confidence interval: 32.51% - 41.96%). At the first contact and at 15 months, MOV were 10.7% and 71.9%, respectively. The non-EPI Penta-Polio booster between 16 and 18 months was not administered to any child. The non-EPI vaccines against typhoid fever and meningitis (ACYW135, AC) were administered to one and two children, respectively ( Table 2 ).

The main individual reasons for missed vaccination opportunities were: lack of communication about non-EPI vaccines (60.71%), parents’ lack of knowledge of the EPI schedule (49.76%), and child illness (25.71%). For health workers, the reasons cited were lack of training on vaccination in the previous two years (81.08%), not systematically checking the health record during consultation and at hospital discharge (79.72%), and stockouts of EPI vaccines at the health center (71.62%). Table 3 shows the reasons for missed vaccination opportunities.

*High cost, insufficient state subsidy for non-EPI vaccines 2, forgot appointment date 2, and vaccine hesitancy 1.

Overall, missed opportunities for vaccination were observed in 37.1% of children attending the Pediatric Department of the CHU-YO. At the first contact and at 15 months, the rates were 10.7% and 71.9%, respectively. The high rate of MOV highlights the efforts needed to improve the extent of national coverage for children, enhance timely vaccination, and ensure greater equity [4] . An analysis using data from Demographic and Health Surveys (DHS) noted that 36% of children aged 12 - 23 months and 24% of children aged 24 - 35 months were fully vaccinated according to the national vaccination schedule [14] . Other authors have found mixed results in the literature. In the Dominican Republic, South Africa, and the Central African Republic, the prevalence of MOV in children under 5 years of age was 43.7%, 27.3%, and 33%, respectively [15] - [17] . In Nigeria, the prevalence of MOV in children aged 0 to 23 months was 36.15% and 32.8% [18] [19] . Higher rates were found in Gambia, by Doctors Without Borders (MSF), in Malawi, in Cameroon and in Burkina Faso, at 60%, 64.6%, 66%, 75.1% and 76%, respectively [6] [7] [11] [20] [21] . The overall frequency of missed opportunities for vaccination in BF remains high and requires research to better understand the reasons for these MOV.

The low MOV rate at the first contact (birth) compared to subsequent contacts could be explained by the systematic vaccination of newborns at birth in the absence of contraindications. The more vaccination contacts increase, the more MOV increases [7] [10] - [12] . This also explains why children did not receive the booster doses for EPI and non-EPI vaccines. Children beyond their second year of life are particularly vulnerable to MOV. It is strongly recommended that vaccination eligibility be assessed as a routine healthcare practice, regardless of the reason for the visit, by screening the vaccination record. Strengthening the implementation of “second year of life” visits and catch-up activities is a proposed strategy to reduce MOV [15] .

The main individual reasons for missed opportunities for vaccination were a lack of communication about vaccines (60.71%), parents’ lack of knowledge of the EPI schedule (49.76%), and illness in children (25.71%). For health workers, the reasons cited were lack of training on vaccination in the previous two years (81.08%), not systematically checking the health record during consultation and at discharge (79.72%), and stockouts of EPI vaccines at the health center (71.62%).

Lack of knowledge and information about vaccines among parents and caregivers was a frequent reason for MOV [9] [12] [20] [22] . Illness and hypotrophy were cited by parents, which led to the postponement of vaccination visits due to benign acute illnesses, antibiotic treatment, or convalescence, which they mistakenly classify as contraindications to vaccination [4] [22] . This highlights the importance of educating parents during medical contacts to correct misconceptions about eligibility (including false contraindications), and to provide basic knowledge about the vaccination schedule and catch-up schedules [4] . It is also necessary to remind mothers of appointments by telephone, home visits, and consultations, and to prevent vaccine stockouts by training health workers at the center in stock management.

The reasons perceived by health personnel concern their knowledge, attitudes, and practices as well as the health system. The lack of training highlights the need for continuous professional development for health workers. In one study, health workers felt that their knowledge of immunization was insufficient or outdated; 83% failed to correctly identify valid contraindications to vaccination [7] . This leads to the failure or inability of health workers to select eligible patients. In addition, the lack of vaccination status checks during routine visits or visits for curative care or other services constitutes missed vaccination opportunities. Stockouts of vaccines and/or vaccination supplies at the health center were also noted, consistent with other authors [20] [23] .

Most missed opportunities are due to non-compliance with established policies and procedures. Previous MOV assessments suggest several common reasons for missed vaccination opportunities in health facilities, which include: the inability of health workers to select eligible patients; perceived vaccination contraindications by caregivers and parents; vaccine shortages; rigid clinical schedules that separate curative services from vaccination areas; and parental or community opposition to vaccination [3] [4] . There is a need to strengthen the training of health workers on vaccination policies and practices, improve caregiver engagement, and ensure that health workers verify vaccination documentation at every healthcare encounter [4] [19] .