Abstract Background China introduced the Supplementary High-Cost Illness Insurance (SHCII) to strengthen financial protection against medical impoverishment. This study assesses its effectiveness and, critically, examines the distribution of its benefits across population subgroups to identify who benefits more. Methods We used 2013 and 2018 survey data from Shandong Province and a difference‑in‑differences design, restricting the sample to hospitalized patients ( n = 3,136). The treatment group comprised patients whose out‑of‑pocket expenses exceeded city‑specific 2018 SHCII thresholds; the control group comprised those below the thresholds. The outcome was Vulnerability to Expected Poverty (VEP). Subgroup analyses were performed by income, urban‑rural residence, healthcare access, and age. Results Patients who benefit from SHCII experienced a significant reduction in VEP relative to those below the threshold (OR = 0.624; average marginal effect = -0.064). The protective effect was statistically significant for low‑income individuals, rural residents, those with healthcare access within 15 min, and adults aged 45 years and above. No significant effect was found for urban residents or for those with poorer geographical access to care. Conclusion Patients who benefit from SHCII experienced a greater reduction in poverty vulnerability relative to those below the threshold, with effects concentrated among low‑income, rural, older, and well‑accessed populations. No significant association was observed for urban residents. The findings from Shandong, where policy parameters are broadly consistent with national guidelines, are likely generalizable to other provinces with similar policy designs and rural healthcare infrastructure. Future research is needed to test how different policy parameters affect the results. Clinical trial number Not applicable.
Fu et al. (Wed,) studied this question.