A multicentre, stepped-wedge, cluster-randomised controlled trial named HAPPEN was conducted in Australia. The research investigated the effectiveness of oral care in preventing non-ventilator hospital-acquired pneumonia (NV-HAP). The study population consisted of patients admitted to hospital environments. The findings demonstrated that improving oral care reduces the incidence of NV-HAP compared with usual care. These outcomes deliver novel and clinically significant evidence for clinical practice. The results provide important information to guide the development of future prevention guidelines. Furthermore, the evidence will help inform hospital infection control policies.