The methods section adheres to the Transparent Reporting of Evaluations with Non-randomized designs (TREND) statement checklist guidelines [22].
Participants
This was a quasi-experimental cohort study using a static-group comparison design with multiple post-test measurements. It was conducted in the maternity ward of the Centre hospitalier universtaire de Sherbrooke (CHUS), located in the Eastern Townships region (Quebec, Canada). Births occurring at the CHUS represent 95% of the total births in the region. During a one-year period, eligible mothers (aged 18 or over, speaking French or English, and living in the Eastern Townships region) who gave birth at the CHUS and the respective newborn infants (twins included) were included in the study. Mothers or newborns requiring acute care were excluded from the study.
Mothers were screened during their postpartum stay in the maternity ward, over regular business hours (8AM to 5PM), in chronological order of delivery. In practical terms, this meant that mothers who had delivered first and who had not been approached by the research team were screened first. This approach was adopted in order to optimize recruitment given the short duration of postpartum maternity ward stays (mean duration = 48 hours). Mothers who agreed to participate signed an informed consent form.
All children whose mothers received the study intervention were assigned to the experimental group, while the static control group included children of mothers who were not approached to participate in the study. Two other groups were considered in this study: the primary refusals group, with children of approached mothers who refused to participate in the study, and the secondary refusal or impossible intervention group comprising children of mothers who agreed to participate but withdrew their consent before receiving the intervention because of fatigue or breastfeeding issues.
Intervention
The MI-based educational intervention followed the Quebec Immunization Protocol [23] and was developed according to the study conceptual framework [15]. Using an MI-specified empathic communication style, it addressed several pieces of information such as the 6 vaccine-preventable diseases (VPD) at 2, 4, and 6 months of life, the effectiveness of vaccines, the importance of the routine immunization schedule, and the fears and side effects associated with vaccination. During 2010 to 2011, the Quebec routine immunization schedule recommended two vaccines at 2, 4, and 6 months of age to protect against diphtheria, tetanus, poliomyelitis, whooping cough, and Haemophilus influenzae type b (Hib), and pneumococcus infections [23]. The intervention content was adapted from two existing theoretical frameworks: 1) the Health Belief Model [24] and 2) the transtheoretical model of behavior change [25]. Based on this composite model, the intervention was adapted to each participating family according to the current intention of the parent to vaccinate his/her newborn at 2 months of age.
The MI session was administered once individually to consenting mothers 24 to 48 hours after the delivery in their rooms by one of 3 clinical research assistants, who had received standardized training on the intervention’s content and MI techniques. The intended duration of the intervention was 20 minutes (Additional file 1).
Objectives
We hypothesized that an individualized educational information session regarding immunization and given during postpartum hospitalization would improve VC for the 2-, 4-, and 6-month vaccines. The aim of the study was to assess the impact of this novel educational strategy based on MI techniques, on the VC of infants at 3, 5, and 7 months of age.
Outcomes
The main outcome measures were the VC of infants at 3, 5, and 7 months of age. The secondary outcome measure was the feasibility rate of the intervention (i.e., the proportion of mothers who received the intervention/mothers who accepted to receive the intervention).
To evaluate the VC of infants, vaccination data were obtained from LOGIVAC, the immunization registry of the Eastern Townships region. This exhaustive registry contains all births that have occurred in the region and records all vaccines administered to residents of the Eastern Townships since 1998, including data for those born outside the region. Thus, all children born in the region, regardless of their vaccination status, are included in the LOGIVAC registry. Vaccination data were extracted by the Eastern Townships Public Health Department for all the participant infants (experimental group), children of mothers who were not approached (control group), and for children of mothers who refused the intervention (primary and secondary refusal groups). Because we had access to nominal data for all the mothers who gave birth at the CHUS, the extraction of vaccination data of infants for all eligible mothers in the study was possible. The extraction of nominal vaccination data and data pairing with the study data was performed by a research agent of the Eastern Townships Public Health Authority, who was not involved with our study and was blinded to the assignation groups of the study.
Determination of the immunization status
The immunization status was determined at 3, 5, and 7 months of age for each eligible infant in order to allow a reasonable time to receive the recommended vaccines at 2, 4, and 6 months, as included in the routine immunization schedule. This one-month delay to assess VC corresponds to the national standards established by the Canadian Immunization Registry Network [26]. A child was considered to have a complete vaccination status if he/she received all vaccines or antigens recommended by the Quebec Immunization Protocol, except for the vaccines against influenza viruses [23].
Assignment method and sample size
Once the immunization status was determined for all children, the main outcome measures (VC at 3, 5, and 7 months) were computed for each study group as the proportion of children with a complete vaccination status among the total number of children in each group. The independent variables, such as mother’s age, length of postpartum hospitalization, cesarean birth, infant’s rank in the family, and hospitalization of the newborn in the neonatology ward during the postpartum stay, were used to assess the comparability of groups and to control for potential confounding factors. In order to identify a statistically significant amelioration of 5% in the VC of infants, and taking into account a VC of 80% [6], a risk of alpha error of 0.05 and a power of 80%, a total of 943 mothers per group should be recruited accordingly with the 3000 annual births at the maternity ward of the CHUS.
Data analysis
Characteristics of included mothers and newborns were analyzed using descriptive statistics such as frequency, mean and standard deviation (SD), and median and interquartile range (IR). These characteristics were compared between experimental and control groups using the χ2 test for dichotomized variables, and the Student’s t-test or Mann-Whitney test for continuous variables both normally and not normally distributed, respectively. Respective VC at 3, 5, and 7 months of age was compared between experimental and control groups using χ2 tests to assess the impact of the intervention. Relative risks (RR) with respective 95% confidence intervals (CIs) were computed for each VC using univariate logistic regressions according to the generalized estimating equations (GEE) procedure. Both per-protocol (PP) and intention-to-treat (ITT) analyses were performed. Furthermore, multivariate regressions with the GEE procedure were realized in the PP and ITT analyses to assess the intervention’s impact on VC adjusted for mother’s age, cesarean birth, birth order, and hospitalization in the neonatology ward. Finally, in order to ascertain the absence of selection bias, the VC at ages 3, 5, and 7 months of the three study groups who did not receive the intervention were compared using χ2 tests. Statistical analyses were performed using IBM SPSS version 20.0 (Armonk, NY) and SAS version 9.3 (SAS Institute Inc., Cary, NC, USA), with statistical significance set at 0.05.
Ethical considerations
Approval for this study was obtained from the CHUS Ethics Committee in Humans Health Research. In addition, we obtained an authorization from the “Commission d’accès à l’information du Québec” (CAI) to have access to vaccination data contained in the immunization registry.