Vaccination coverage and factors associated with adherence to the vaccination schedule in young children of a rural area in Burkina Faso

Background: Vaccination is an important tool for reducing infectious disease morbidity and mortality. In the past, less than 80% of children 12–23 months of age were fully immunized in Burkina Faso. Objectives: To describe coverage and assess factors associated with adherence to the vaccination schedule in rural area Burkina Faso. Methods: The study population was extracted from the Nouna Health and Demographic surveillance system cohort. Data from four rounds of interviews conducted between November 2012 and June 2014 were considered. This study included 4016 children aged 12–23 months. We assessed the effects of several background factors, including sex, factors reflecting access to health care (residence, place of birth), and maternal factors (age, education, marital status), on being fully immunized defined as having received Bacillus Calmette–Guérin (BCG), three doses of diphtheria–tetanus–pertussis and oral polio vaccine, and measles vaccine by 12 months of age. The associations were studied using binomial regression to derive prevalence ratios (PRs) in univariate and multivariate regression models. Results: The full vaccination coverage increased significantly over time (72% in 2012, 79% in 2013, and 81% in 2014, p = 0.003), and the coverage was significantly lower in urban than in rural areas (PR 0.84; 0.80–0.89). Vaccination coverage was neither influenced by sex nor influenced by place of birth or by maternal factors. Conclusion: The study documented a further improvement in full vaccination coverage in Burkina Faso in recent years and better vaccination coverage in rural than in urban areas. The organization of healthcare systems with systematic outreach activities in the rural areas may explain the difference between rural and urban areas. The study was conducted in the area of the Nouna Health and Demographic Surveillance System (HDSS). Nouna HDSS is located in the North West of Burkina Faso, in Nouna Health District 300 km from the capital Ouagadougou. The research area is 1775 km2 [22]. In 2014, the HDSS comprised about 100,000 inhabitants residing in Nouna town and the surrounding 58 villages. The predominant economic activity in the region is agriculture. The annual growth rate is 2.8% with a fertility rate of 6.2. Mortality in Nouna HDSS is high. The infant mortality for 2010 was 27/1000 live births, and the under-five mortality was 81/1000 live births [23]. The area has 16 peripherals health centres. The study population for the present study was extracted from the HDSS cohort. Data from four rounds of interviews conducted between November 2012 and June 2014 were used. The study included children who were between 12 and 23 months old at the time of the visit, were alive, and had their vaccination card seen. If a child had more than one visit, the information obtained at the first visit was used. The routine vaccination programme in Burkina Faso in 2010–2014 included five different vaccines for the prevention of nine pathogens: (1) BCG against tuberculosis, (2) Oral Polio Vaccine (OPV), (3) Pentavalent Vaccine against diphtheria, tetanus, pertussis, hepatitis B, and Haemophilus influenzae type b (Penta), (4) yellow fever vaccine, and (5) MV. The recommended vaccination schedule in Burkina Faso was BCG and first dose of OPV (OPV0) at birth; three doses of Penta and OPV at 8, 12, and 16 weeks; and measles and yellow fever vaccination at 9 months of age. Children living in villages with a peripheral health centre (CSPS) received routine vaccinations during monthly vaccination sessions. The CSPS also arranged vaccination sessions in villages in their catchment area once per month as well as catch-up sessions for those who missed the normal sessions at the CSPS or outreach days in the community. The vaccines are provided through UNICEF and GAVI, and are free of charge for the parents. Vaccines are registered on a health card, which is given to the mother at her first antenatal care visit. The card is used for both the mother’s information during the pregnancy and for the child’s information, vaccinations, and birth weight of the child. Mothers who do not attend antenatal care are provided a vaccination card at the first vaccination contact for the child. The collection of vaccination data took place at the regular vital-event registration rounds in the HDSS. The HDSS rounds collect routine data at 3 times/year visits from all households of the HDSS area. During these visits, vaccination data were collected from the vaccination cards for all children younger than 3 years of age. At all visits, the date of the visit and whether the child’s health card was seen were recorded. Provided the card was seen, the dates of all vaccines were noted on the child’s HDSS form. At a following round, the field assistant brought forms to the household of the individual child with preprinted dates of the vaccinations already registered. The field assistant inspected the card and updated the child’s vaccination information. When a round finished in a village, the questionnaires were sent to the data-entry team. Data were entered in Microsoft Access 2007. Data-consistency checks were carried out during data entry where the system prompted the user if impossible values were entered (i.e. date of vaccination before date of birth). During data entry, questionnaires with missing or unclear information were sent back to the field supervisors and, if necessary, to the interviewers for correction. Following data entry, checks were made on consistency. Further validation was carried out through duplicate data entry of 5% of all questionnaires by the data-entry supervisor. Information on background variables (maternal age, maternal education, place of birth, occupation, religion, marital status, season of birth, area of residence, and ethnic group) was collected during the HDSS rounds. We determined the vaccination coverage of all antigens by 12 months of age and ages for median coverage as the age where 50% of children had received a particular vaccine. Vaccination status was determined based on the first visit to a child aged 12–23 months in 2012–2014 at which vaccination status was assessed by inspecting the vaccination card. The children who did not present a vaccination card at the time of the visit and the children who migrated or died before the visit were not included in the analysis. We compared the distribution of background factors for children who were included and children who were not included. We defined a fully immunized child (FIC) as completion of the core EPI vaccinations by 12 months of age not including OPV0 at birth, since this vaccine is only given during the first weeks of life, and yellow fever vaccine, which is not globally recommended by WHO [7]. To describe adherence to the vaccination programme, we subdivided the FIC children into FIC in sequence (FICIS) which was defined as the WHO recommended sequence of vaccinations, i.e. BCG before OPV1, OPV1 = Penta1, OPV2 = Penta2, OPV3 = Penta3, and Penta3 before MV. If this sequence was violated, children were defined as FIC out of sequence (FICOS). We further described the children missing one or more vaccines by the number of vaccines missing by 12 months of age and subdivided this into different antigens. Missed opportunities were defined as contacts with the health system where a vaccine dose could have been given, but where it was not received. For BCG, we defined a contact with the health system as either being born at a health facility or having received other vaccines but not BCG. Missed opportunities for later vaccines were time points where some, but not all, age-appropriate vaccines were given, i.e. children missing Penta3 and MV, who received only the one of the vaccines when seeking vaccination after 9 months of age. Our primary analysis focused on coverage and factors associated with being FIC versus not FIC. Associations between background factors and vaccination coverage were studied using binomial regression in univariate and multivariate regression models. A log-link function was used to obtain prevalence ratios (PR) using the command ‘binreg’ in Stata. The estimated PR and corresponding 95% confidence intervals are presented together with the p-values from the overall test (Wald) of no association between the factor and FIC. Similarly, we assessed the factors associated with being FICIS among children who were FIC. Data were analysed using STATA V.12.0. This study was part of the OPTIMUNISE project, which was approved by the National Ethics Committee in Burkina Faso and by the local Ethical Committee in Nouna. Informed community consent was sought for the implementation of the additional survey questionnaire during routine HDSS procedures.