Completeness of the vaccination schedule in the population evaluated in the present study was 52.1%, far below the goal of 95% established by the National Immunization Program and also below the coverage achieved in infants under 12 months of age in Recife in 2015 with respect to the third dose of the diphtheria-tetanus-acellular pertussis-hepatitis B virus-inactivated poliovirus and Haemophilus influenzae type B (pentavalent DTaP-HB-IPV-Hib) vaccine .
The pentavalent vaccine is considered a good indicator of the complete vaccination schedule, since it reflects the capacity of the healthcare service to reach the same child and deliver the series of three doses required . The percentage of coverage found in this community is comparable to statistics for countries classified as having medium to low human development indices such as Pakistan, India and Ethiopia. In those countries, the rates of complete vaccine coverage for children of 12 to 23 months of age were 51.3% , 53%  and 58.4% , respectively.
Possible interruptions in the supply of immunobiological agents in healthcare services, due to brief shortages, particularly with respect to the vaccines most recently included in the immunization schedule, could have interfered with the results obtained, as found in a study conducted to analyze the coverage of new vaccines offered in the vaccination schedule . The restriction considering the child’s age in months and days for application of the oral vaccine against human rotavirus, justified for safety reasons, may also constitute a relevant factor.
The significant reduction in the incidence of vaccine-preventable diseases in recent decades could have changed parents’ perceptions regarding the benefits of vaccinating children in relation to potential adverse events, despite the fact that these are rare . Missing the opportunity to vaccinate children attending a healthcare service for another reason or even when they are just accompanying their mothers also contributes to the low rates of immunization coverage .
An inverse association was found in the present study between completeness of the vaccination schedule and the child’s age. This finding is in agreement with the results of a prospective cohort study conducted in the Brazilian state of Maranhão in which incomplete vaccination increased as a function of the child’s age . A study conducted with hospitalized children in Recife reported similar findings . This could be attributed to the fact that most of the vaccines included in the vaccination schedule are given in the first year of life, especially up to six months, on dates that
match with the child’s routine check-up visit. We emphasize that the probability of having a lesser delay in children under six months may have been influenced by the greater number of outpatient visits for clinical monitoring during this period when compared with older children, which may have led to some classification bias [26}. After this age, monitoring at the healthcare unit becomes less frequent and the risk of incomplete vaccination schedule increases in the older age group. If so, parents' attention may be diverted to a younger sibling [5,22].
Nonetheless, in communities in which the Family Health Strategy is in operation, completeness of the vaccination schedule should not be linked exclusively to the child going to the healthcare unit, but should also be associated with monthly home visits by community health agents as part of their attributions in promoting health within their defined geographical area . Another family health strategy activity that encourages vaccination is actively searching for children who have failed to attend for their vaccination on the scheduled date by ensuring that the control card in the vaccination room is correctly filed and used within an appropriate timeframe and in a programmed manner .
The finding of an association between complete vaccination schedule and maternal education level corroborates another reports [3,5,7,9,23]. The association between poor maternal schooling and incomplete vaccination can be explained by the fact that education level influences knowledge on the different types of vaccine, why they are necessary, their availability, recommendations, benefits and risks . This finding could be used to assist the health care team in identifying and monitoring more closely the children of mothers with low schooling in order to implement their vaccination. It signals that this mother needs to receive more attention from them by being available and providing clarification on the importance of updating vaccines in a simpler and understandable way for her. It can also contribute to directing dissemination strategies and encouraging vaccination through more visual than textual communication in order to reach this population in an efficient way. Nevertheless, there is controversy on the subject, as shown in another state in Brazil where vaccination coverage was better among the children of relatively uneducated mothers, probably due to their need to maintain the child’s vaccination card up-to-date to ensure continuity of their benefits within the Family Benefit Program .
No association was found between social class, classified according to family income, and completeness of the vaccination schedule, and this could be a consequence of the homogeneity of income in this population, preventing comparisons between them. There was no family in social class A, a small percentage classified as B and the majority of families belonged to class C and DE with lower incomes. About this, a study conducted in the capital cities of the northeastern states of Brazil showed lower rates of vaccination coverage in children belonging to social class A, i.e. those with the highest family income .
No association was found between maternal age and completeness of the vaccination schedule. Nevertheless, a recent publication showed that incomplete vaccination was 26% more common among children of adolescent mothers .
In the present study, no association was found between any of the factors related to maternal prenatal care and completeness of the vaccination schedule. This finding contradicts the results of another study showing that maternal prenatal care initiated only in the third trimester of pregnancy and having attended fewer than six prenatal consultations were factors associated with incomplete childhood vaccination . In the present sample, however, almost all the mothers interviewed had received prenatal care, which made comparison between groups impossible.
A limitation of this study is that the evaluation failed to take into account the types of vaccine responsible for the rates of incomplete vaccination schedule, i.e. whether the newer or older vaccines were more likely to be missed. On the other hand, a strongpoint lies in the fact that the data of vaccine administration were obtained directly from the child’s personal health record, thus minimizing the possibility of biases that can occur when data is provided verbally. The fact that an evaluation of internal validity was performed represents another strong point, since this allows the present findings to be compared with results for the same population in different surveys or indeed for the findings to be extrapolated to a population with similar characteristics.
This was the first study to use an epidemiological approach with non-aggregate data at the community level and the results could be proposed as baseline data to monitor completeness of the vaccination schedule in populations living in areas with similar socioeconomic characteristics in Brazil and in other developing countries.
The associated factors identified need to be submitted to a more in-depth analysis by means of a qualitative study focusing on the reasons for incomplete vaccination schedule. Such further evaluation would take into consideration the attitude of the parents or guardians in relation to the child’s vaccination.