Discussion
SECONDARY
This study shows that an educational intervention on vaccination of newborns using MI with mothers in maternity wards in France was significantly associated with a 32.7% reduction in their VH score and an 8.5% increase in their intention to vaccinate their infants at 2 months of age. This was observed in a context where 11 childhood vaccines are required for admission to daycare and schools. Stratified analyses found the MI intervention's effect on VH and VI was greatest in mothers with a high initial VH level and differed only slightly by social deprivation level (measured through education level and perceived financial situation). The D-I-D analysis estimated the net decrease in VH due to the MI intervention at 5.8/100 points and the net increase in VI at 0.6/10 points. The D-I-D stratified analyses indicated a still higher net effect of MI on VH and VI in mothers with a higher initial VH level and revealed a differential effect by social deprivation level: the decrease in VH related to MI was only found in mothers with a low level of education, while the increase in VI was only found in mothers with a higher level of education. Most mothers in both groups were satisfied, although the control group had more ‘somewhat’ responses (24.6–31.1%, versus 9.4–17.5% in the MI group).Comparisons with the Quebec study results show a similar magnitude of the MI intervention's effect on mothers’ VH. It was −33% in our study, −40% in the PromovaQ study, and −29% in the EMMIE programme [Our study adds to the two aforementioned studies the use of D-I-D, to estimate the intervention's net effect compared with the control group. We found that MI's impact on both VH and VI remained significant, and at a relatively high level of magnitude compared with other educational approaches [Our results suggest that MI could reduce VH especially among mothers who are part of socially deprived populations, whose VH was highest in our study. The MI approach (listening, non-judgemental) probably enabled these mothers to better express their concerns and allowed midwives to respond more appropriately than a standardised leaflet could allow (no significant VH reduction found among the less educated in the control arm). This suggests that MI may be useful for addressing social inequalities in vaccine acceptance [Our results regarding mothers' satisfaction are similar to those found in the PromoVac study and EMMIE programme [This study has several limitations. We measured intentions to vaccinate rather than actual vaccination status since childhood vaccines were almost all required at the time of survey and, as a result, vaccination rates were high, which would have prevented us from showing MI's effect, if any, on infant vaccine coverage. Moreover, 21% of the 257 women who refused participation were motivated by lack of interest in vaccination. Selection and/or reporting bias(es) leading to a false conclusion of a significant difference between the groups nonetheless seem(s) unlikely, as consent to participate was obtained prior to randomisation and few mothers refused to take part because of disinterest in vaccination (n = 53 mothers compared with 733 included). The short follow-up period at the hospital raises the possibility of a Hawthorne effect in both groups. Moreover, because the study could not be anonymised and the mothers spent 10–30 min talking with a midwife in the MI arm, a differential Hawthorne effect leading to an overestimation of MI's effect seems possible [The study has several strengths that minimise its potential biases. The similarity of demographic characteristics and initial VH scores between the two groups validates the randomisation process. The very low rate of secondary refusals (after randomisation) indicates participants' acceptance of this procedure. Finally, our protocol is close to that of the published Promovac and PromovaQ studies and EMMIE programme. In particular, we used the same validated instrument for the main judgement criteria (PACV) [