Abstract: We included 38 studies, mostly from high-income countries, many of which explored mothers' perceptions of vaccine communication. Some focused on the MMR (measles, mumps, rubella) vaccine. In general, parents wanted more information than they were getting (high confidence in the evidence). Lack of information led to worry and regret about vaccination decisions among some parents (moderate confidence). Parents wanted balanced information about vaccination benefits and harms (high confidence), presented clearly and simply (moderate confidence) and tailored to their situation (low confidence in the evidence). Parents wanted vaccination information to be available at a wider variety of locations, including outside health services (low confidence) and in good time before each vaccination appointment (moderate confidence). Parents viewed health workers as an important source of information and had specific expectations of their interactions with them (high confidence). Poor communication and negative relationships with health workers sometimes impacted on vaccination decisions (moderate confidence). Parents generally found it difficult to know which vaccination information source to trust and challenging to find information they felt was unbiased and balanced (high confidence). The amount of information parents wanted and the sources they felt could be trusted appeared to be linked to acceptance of vaccination, with parents who were more hesitant wanting more information (low to moderate confidence). Our synthesis and comparison of the qualitative evidence shows that most of the trial interventions addressed at least one or two key aspects of communication, including the provision of information prior to the vaccination appointment and tailoring information to parents' needs. None of the interventions appeared to respond to negative media stories or address parental perceptions of health worker motives. We have high or moderate confidence in the evidence contributing to several review findings. Further research, especially in rural and low- to middle-income country settings, could strengthen evidence for the findings where we had low or very low confidence. Planners should consider the timing for making vaccination information available to parents, the settings where information is available, the provision of impartial and clear information tailored to parental needs, and parents' perceptions of health workers and the information provided.

Plain-language summary: We included 38 studies in our review. Most of the studies were from high-income countries and explored mothers' perceptions of vaccine communication. Some of the studies also included the views of fathers, grandmothers and other caregivers. In general, parents wanted more information than they were getting (high confidence). For some parents, a lack of information led to worry and regret about their vaccination decision (moderate confidence). Parents wanted balanced information about both the benefits and risks of vaccination (high confidence), presented in a clear and simple manner (moderate confidence) and tailored to their situation (low confidence). Parents wanted vaccination information to be available outside of the health services (low confidence). They wanted this information in good time before each vaccination appointment and not while their child was being vaccinated (moderate confidence). Parents viewed health workers as an important source of information and had specific expectations of their interactions with them (high confidence). Poor communication and negative relationships with health workers sometimes impacted on vaccination decisions (moderate confidence). Parents generally found it difficult to know which vaccination information source to trust and found it difficult to find information that they felt was unbiased and balanced (high confidence). The amount of information parents wanted and the sources they felt they could trust seem to be linked to their acceptance of vaccination, with parents who were more hesitant wanting more information (low to moderate confidence). How up-to-date is this review? We searched for studies published before 30 August 2016.