What Primary Care mechanisms impact mortality in children under five?

Abstract Background Countries with health systems centered around Primary Health Care tend to achieve better results in maternal and child health, especially in relation to lower morbimortality rates due to preventable causes and health inequalities. However, Primary Health Care is a complex, multifaceted intervention, making it fundamental to understand how its mechanisms address relevant population health outcomes. This paper seeks to identify, classify, evaluate and summarize existing evidence on Primary Health Care mechanisms that influence mortality in children under five, based on a critical realistic epistemology, to inform decision-making. Main body A realist, five-step synthesis was conducted to grasp such mechanisms. As the first step, a theoretical model depicting comprehensive primary health care was developed, based on the analysis of documents from Brazilian regulation on maternal and child health care. The next steps involved an article search, selection and review of relevant sources, extraction and synthesis of evidence, and, finally, the reaching of a consensus on the final theoretical model in step five, based on the evidence encountered in the selected studies. One hundred and thirty-five studies were included, covering research in several countries, exemplifying primary health care as an effective intervention to improve children’s health in different contexts. Additionally, this review revealed that specific interventions, based on selective primary health care, are less powerful, signaling the importance of a systemic approach that acknowledges the interconnection and interaction of Primary Health Care’s multiple components. Furthermore, significant gaps in existing evidence related to specific structuring components of Primary Health Care and how they affect child health, including, but not limited to, planning and organization of services and work processes, or the referral and regulation system. Conclusions We envision that the results of this study may support decision-makers with a deeper understanding of Primary Health Care and how it can be most effective in the improvement of the population’s health. We recommend further studies addressing Primary Health Care as a complex and comprehensive intervention, in different contexts, specifically in relation to the components and indicators of our theoretical model.