Abstract
BACKGROUND: Mexico replaced Seguro Popular—its public insurance for people without formal employment—with the Instituto de Salud para el Bienestar (INSABI) in 2019. How this policy change relates to insurance coverage and health-care use among older adults has not been examined with nationally representative longitudinal data. METHODS: Data came from 12 759 participants in the Mexican Health and Aging Study who were interviewed in 2018 and 2021 and were 50 years and older. Descriptive statistics documented changes in insurance status and provider type. Three multivariable models assessed: (1) factors associated with becoming uninsured (binary logistic regression), (2) the relation between insurance loss and provider type in 2021 (multinomial logistic regression), and (3) the likelihood of switching from public to private care between waves (binary logistic regression). Predictors included age, sex, community size, education, self-rated financial status, and six doctor-diagnosed conditions. RESULTS: The share of respondents without insurance rose from 9% in 2018 to 26% in 2021, while coverage through Seguro Popular or its successor INSABI fell from 30% to 11%. More than half (53%) of 2018 Seguro Popular enrollees became uninsured by 2021. Living in a community with fewer than 2 500 inhabitants (odds ratio = 3.5), having at most six years of schooling (odds ratio = 1.7), and reporting poor finances (odds ratio = 2.5) were strong correlates of losing coverage. Among those who became uninsured, the relative likelihood of using private rather than Secretaría de Salud facilities increased markedly (relative risk ratio = 1/0.61). Among participants who used public providers in 2018, losing insurance was associated with an 80% higher probability of switching to private care by 2021. CONCLUSIONS: Between 2018 and 2021 the proportion of Mexicans aged 50 years and older who lacked insurance nearly tripled, and health-care use shifted decisively toward the private sector, especially among rural, less-educated, and economically disadvantaged groups. Ensuring clear affiliation mechanisms and improving the quality and availability of public services are pressing priorities if Mexico is to prevent widening financial and access disparities under the post-Seguro Popular system. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12913-025-13673-x.