We identified 116 boys and 96 girls (Table 2); the sex ratio was 1.21. The average age at enrolment was 16.35 ± 6.95 months, with extremes of 6.01 and 30.09 months. Children aged 12 to 24 months represented 47.64% of the population (Table 2). Eighty-five or 40.10% of the children’s mothers had not attended school, and 24.50% had primary education (Table 2). The children were born at the university hospital, in other hospitals and in outlying health facilities, in 22.2%, 17.0% and 36.8% respectively (Table 2). Thirty children (14.1%) were born at home.

*Regional hospital center and general hospital. **Urban health center and rural health center.

Two hundred and five children received the BCG vaccine. The median age at the time of vaccine administration was 6 days with an interquartile range of [2.5; 13.5] days. This vaccine was administered before the age of 1 month in 93.17%; 11 children received the vaccine at an age between 1 and 3 months and 3 others beyond 3 months. The average age at administration of the 1st dose of combined and co-administered vaccines was 7.66 ± 3.81 weeks with extremes of 2.71 and 38.28 weeks and the median was 6.71 weeks. The average age at administration of the 2nd dose of these vaccines was 12.88 ± 3.95 weeks with extremes of 7.28 and 37 weeks and the median was 11.57 weeks. The median at the time of administration of the 3rd dose of the latter was 16.57 weeks with an interquartile range of [15.5; 19.5]. The average age at VAA administration was 9.92 ± 1.65 months with extremes of 8.37 and 19.08 months. The average age at VAR dose administration was 9.86 ± 1.60 months with extremes of 8.14 and 19.08 months.

Thirty-two children out of 212 could not receive the measles and yellow fever vaccines which are administered at the age of 9 months. The number of children who should therefore receive these vaccines was 180. The proportion of children for each EPI vaccine antigen received or not is illustrated in Figure 1. Only one child did not receive any vaccine. Four received only the BCG vaccine. Four others, in addition to the BCG vaccine, only received the first 2 doses of the combined and co-administered vaccines. The number of doses not received of the different EPI vaccine antigens was 119. Seventy-five mothers of children who did not receive these vaccine doses had never been to school and 32 had primary school education (Table 3). The proportions of children whose vaccination schedule was up to date for age depended on the place of birth. These rates were 89.4% (42/47) at the university hospital, 72.2% (26/36) in other hospitals, 80.8% (63/78) in peripheral health facilities, 90.5% (19/21) in private structures and 53.3% (16/30) at home.

Missed vaccination opportunities were found in 79 cases. The main reasons were neglect of the mother (49.36% of cases), difficulties in accessing centers (means of transport and financial problems) in 17.72% of cases, illnesses of the child (13.92%) and ignorance of the mother (10.13%). The other reasons (8.87%) noted were the unavailability of the mothers, the lack of vaccine doses and the father’s refusal (Figure 2). Vaccines were not always administered on dates recommended by the Enlarge Program of vaccination. The explanations listed were linked to the mother (ignorance, travel, illness), to the health structure (limited number of daily doses administered or stock shortage), to tradition (some parents of children who did not receive the BCG vaccine at birth were waiting the baby’s “coming out” ceremony which was generally done on the 7th day of life to mark the official welcome of the child, in certain communities).

We observed a slight male predominance which could be the simple effect of chance. More than 93% of children received the BCG vaccine before the age of one month. This high rate of application of the EPI recommendations relating to the BCG vaccine has been favored by the numerous vaccination campaigns. The BCG vaccine remains justified in risk groups. In this case, it should be done from birth or during the first month of life [6] . In our study, the 3 doses of combined and co-administered vaccines (DTP-HepB-Hib + OPV + PCV 13) were not received in more than 50% of cases on the dates indicated by the vaccination schedule (respectively 6, 10 and 14 weeks). They were, for the most part, administered with a delay. The median ages at the time of receiving these vaccines were 6.71, 11.57 and 16.57 weeks, respectively. If the recommended times between the administration of two doses of the same vaccine cannot be shortened at the risk of an insufficient immune response, extending these times does not pose any problem in terms of vaccine effectiveness [7] . It is therefore unnecessary to repeat the entire schedule in the event of an injection delay, however respecting the vaccination schedule allows the earliest possible protection [7] [8] . The age of the children at the administration of VAR and VAA was in the majority of cases less than 10 months; which was consistent with the age recommended by the EPI which is 9 months. The dates for vaccinations, although mentioned in the children’s health records, were not always respected by the children’s parents. These different results could reveal inattention or forgetting of vaccination dates by some parents or reflect a lack of awareness of the benefits of vaccines among others. The effective involvement of all health professionals, through the systematic verification of vaccines during medical visits, could help resolve the problem of forgetting vaccination dates, especially since 40.10% of mothers of children in our workforce do not had not been to school and 24.50% were at primary level.

The rate of vaccinated children in our study differed from one vaccine to another. The observed values evolved in a descending order going from the 1st dose of combined vaccines (normally scheduled for the 6th week of life) to the administration of the yellow fever and/or measles vaccine (normally scheduled for the 9th month of life). These figures remained above 95% for the BCG vaccine and the first 2 doses of combined and co-administered vaccines, and above 90% for the 3rd dose of combined and co-administered vaccines. Although these vaccines are sometimes carried out late, the rate of vaccinated children was higher than the objective set by the EPI in our country in its operational action plan at the end of 2016 [5] . Our results could be the result of multiple awareness campaigns organized in our country. On the other hand, the rate of completion of yellow fever and measles vaccines (77.8%) was lower than the 90% limit imposed by the EPI in Côte d’Ivoire [5] . This observed discrepancy could be explained by a forgetting of the date of the vaccines in relation to the long wait, estimated at around 6 months, between the dates planned for the last dose of the combined vaccines (14 weeks of life) and that (9 months) yellow fever and measles vaccines (9 months). Our figures nevertheless remained higher than those of Nguefack et al., who in a study carried out in 2016 in Yaoundé, had also noted a decrease from 91.7% to 71.4% concerning the production rates of vaccines ranging from the BCG vaccine to the AAV [9] . In Andriatahina’s series, the low measles vaccination coverage was explained by the measles epidemic that occurred in Madagascar from the end of 2018 [10] . Very high vaccination coverage could have prevented the outbreak of the epidemic [11] . Given the high level of contagiousness of the disease, the elimination of measles required that 95% of the population be uniformly immunized across the territory [12] [13] . The low coverage rate in our various developing countries will not make it possible to achieve these objectives if the weaknesses in the implementation of the EPI are not identified. The different rates of vaccines administered were also influenced in our study by the level of education of the mothers. In fact, 75 of the 119 vaccine doses not received by children were allocated to children whose mothers had never been to school. The children of higher level mothers had all received all vaccines from the 1st contact to the 4th contact, that is to say from the BCG vaccine to the 3rd dose of combined and co-administered vaccines. Andriatahina [10] made the same observation. For Randriatsarafara et al., the low level of education limited the understanding of messages related to the practice of vaccination [14] . However, there could be reasons, other than the level of education of the mothers, which would explain the fact that in our series compliance with the EPI schedule remained a problem, as the child progressed in age, as well as among non-educated parents than educated ones due to forgetting. Thus, two children of mothers at a higher level had received neither the yellow fever vaccine nor the measles vaccine. In Andriatahina’s series, vaccination status was linked to rank among siblings; he noted that the first child born in a family received the maximum number of doses [10] unlike Nguefack [9] for whom it was rather the first of the siblings who did not have an up-to-date vaccination schedule. Furthermore, we noticed a variation in vaccination status depending on the children’s places of birth. Indeed, the proportion (89.4%) of children born at the university hospital having an up-to-date vaccination schedule was higher than that (53.3%) of children born at home. However, this rate of vaccination completeness was not proportional to the level of care offered by the different health establishments, because the percentage of vaccination completeness (80.8%) of childrenborn in other hospital structures was lower than that (90.5%) of childrenborn in peripheral health facilities in ourstudy. All these findings led us to question the reasons for non-compliance with the vaccination schedule.

Missed vaccination opportunities also differed from one vaccine to another. Non-compliance with EPI recommendations was mainly represented by mothers’ negligence or forgetting vaccination dates, inaccessibility of centers, mothers’ ignorance and child illnesses. Not all childhood illnesses should constitute a barrier to the administration of vaccines. Common acute illnesses are not, in the majority of cases, a contraindication [15] . There may be temporary contraindications to the administration of vaccines, such as acute febrile illness [7] . The other causes of non-compliance with EPI recommendations were: the unavailability of mothers, the shortage or limited stock of certain vaccines in particular the BCG vaccine and the VAA, and the father’s refusal. These reasons highlighted the need to increase parental awareness of the role of vaccines in prevention diseases. The information provided must be clear and objective [16] and take into account the socio-cultural background of the parents. The limited stock of BCG vaccine or AAV, with the corollary of repeated unavailability of vaccines at each appointment, could be the cause of discouragement mothers and would also cause vaccination delays. These observed delays were caused by the same reasons as those of non-vaccination, but to different proportions. Bobossi-Serengbé et al., in a study carried out in 2011 in Bangui (Central African Republic), reported that missed vaccination opportunities were lower in health structures that carried out vaccination on fixed days compared to those which carried out it every days [17] . In the series by Pouth et al., the mother/nurse’s failure to master the vaccination schedule was the predictive factor most significantly associated with incomplete vaccination [18] . Compliance with the vaccination schedule therefore requires strengthening public awareness of the benefits of vaccination. This awareness raising of parents should also be done upstream during the various prenatal consultations (CPN) hence the need to convince women to attend the different health centers during pregnancy, the main means of access to the right information for the protection and harmonious development of their future baby. The various pediatric consultations should also be the ideal time to correct the various deviations concerning both the absence of vaccination and delays noted. It would also be useful to intensify the advanced and mobile vaccination strategy by developing a vaccination program based on fixed days and dates known by the populations concerned. Above all, we should increase communication methods by conveying information through voice messages in our vernacular languages and by popularizing the use of electronic notebooks through vaccine dates via written and voice telephone messages. In addition, strengthening social mobilization through the involvement of leaders of Civil Society Organizations (CSOs) would play a big role in the transmission of information [19] . The establishment of an emergency plan for managing the supply of EPI vaccines is the guarantor of the successful implementation of strategies aimed at optimal vaccination coverage.