By the time they reach adulthood, 61% of children in the United States will have been covered by Medicaid or the Children’s Health Insurance Program (CHIP), according to a groundbreaking microsimulation study conducted by researchers at the Harvard T.H. Chan School of Public Health. This first-of-its-kind analysis models individual insurance trajectories from birth through age 18, revealing important insights into the dynamics of health coverage during childhood in the U.S., a nation characterized by a notoriously fragmented health insurance system. The research reveals not only the broad reliance of American children on public insurance programs but also highlights significant vulnerabilities and disruptions that many young people face throughout their formative years.
Tracking the health insurance experiences of children in the U.S. has historically been plagued by fragmented claims data and limited survey follow-up periods, restricting the ability of researchers to capture long-term trends and gaps. The new study navigates these challenges by integrating national natality records with socioeconomic, demographic, and insurance data sources into a sophisticated microsimulation model. This computational approach simulates individual insurance status trajectories spanning birth to adulthood under policy conditions reflective of the mid-2010s to just before the COVID-19 pandemic emergency policies were enacted, providing a robust baseline to understand coverage dynamics.
One of the most striking findings of this model is the prevalence of intermittent insurance coverage among children. Despite the widespread use of Medicaid and CHIP, 42% of children experience at least one gap in coverage before turning 18. These disruptions can have severe ramifications, as interruptions in insurance correlate with delayed medical care, unmet health needs, and worsened long-term outcomes. The study indicates that continuity of coverage remains a pressing and unresolved challenge within the current system.
Geographic and policy variations further exacerbate these disruptions. Children born in states that did not expand Medicaid under the Affordable Care Act are disproportionately affected, with 59% experiencing coverage gaps, compared to 36% in states that expanded eligibility. This disparity underscores the critical role that state-level policy decisions play in shaping health equity and access. Moreover, states that impose more restrictive income eligibility thresholds for Medicaid and CHIP see higher rates of insurance discontinuity among children, illustrating how policy design directly influences coverage stability.
These findings arrive at a pivotal moment as federal policy shifts threaten to reshape Medicaid’s landscape dramatically. In July 2025, the Centers for Medicare and Medicaid Services ceased approving Section 1115 waivers allowing multiyear continuous eligibility for children, a move expected to increase coverage churn. Coupled with a major federal budget reconciliation bill that projects a $1 trillion cut to Medicaid funding and a 10 to 15 million decrease in enrollment, the potential impact on children’s insurance security is profound. The study’s authors caution that these policy changes could exacerbate existing gaps, leading to greater numbers of uninsured children nationwide.
The study’s lead author, Ye Shen, a doctoral student specializing in health policy at Harvard, emphasizes the importance of this research as a baseline for future evaluations. “Our model offers the first comprehensive view of insurance coverage across childhood in the United States, allowing policymakers and advocates to measure the real-world consequences of proposed Medicaid policy changes,” Shen noted. The model’s individual-level simulation approach captures complex insurance pathways and transitions, thereby informing nuanced policy interventions tailored to reduce coverage instability.
Beyond eligibility cuts and funding reductions, the researchers point to additional mechanisms through which children’s coverage may erode. Increased verification requirements, work mandates for parental Medicaid eligibility, and state-level program reductions all have the potential to trigger cascading losses of coverage for both children and their families. Noncitizen children, a group already facing significant barriers, are particularly vulnerable to these policy shifts. These spillover effects amplify the risks that systemic fragmentation poses to childhood health outcomes.
The implications of this study stretch beyond simple insurance metrics. Continuity in Medicaid and CHIP coverage is foundational to ensuring timely preventive care, chronic disease management, and adequate developmental support for children. The model’s revealing of nearly half of all children experiencing coverage breaks speaks to persistent systemic failures that undermine these health goals. Addressing these gaps demands concerted policy action to stabilize and streamline public insurance programs for vulnerable youth populations.
Technically, the microsimulation developed by the Harvard team innovatively synthesizes diverse national datasets, including birth records and multiple health surveys, weaving them into a dynamic longitudinal framework. This approach overcomes typical data silos and short-term snapshots, allowing researchers to simulate realistic insurance pathways under varying policy conditions. Such simulation modeling is rapidly becoming an indispensable tool in health policy research, enabling predictions about outcomes under different legislative scenarios before they unfold in real life.
The work contributes to an expanding literature that increasingly uses computational modeling to forecast the health and economic effects of insurance policies. In a system as complex and variegated as the U.S. health insurance market, traditional empirical studies often lack the temporal depth or breadth to capture important transitions and disparities. Microsimulation thus bridges this gap, providing policymakers with rigorous forecasts to guide decisions that impact millions of children’s lives.
Published in the prestigious journal JAMA on September 24, 2025, this study arrives amid vigorous national debates on Medicaid’s future. Its detailed, evidence-based insights challenge policymakers to consider not only cost containment but also coverage stability. The researchers call for policies that prioritize continuous eligibility and guard against coverage interruptions, recognizing these as essential to safeguarding the health trajectories of children throughout their development.
In conclusion, this research sheds critical light on the complexity and fragility of childhood health insurance in the United States. By illuminating who relies on Medicaid and CHIP, where coverage gaps occur, and how policy environments influence these patterns, it elevates the discourse beyond headline enrollment numbers. The future of American children’s health insurance depends on policies informed by such granular, forward-looking research, aimed at securing uninterrupted access to care during the formative years that shape lifelong well-being.
Subject of Research: Not applicable
Article Title: Insurance Dynamics During Childhood in the Fragmented US Health System
News Publication Date: September 24, 2025
Web References: http://dx.doi.org/10.1001/jama.2025.15488
References: Shen, Y., Sommers, B. D., Hatfield, L. A., Hayes, C., Panya, A., & Menzies, N. A. (2025). Insurance Dynamics During Childhood in the Fragmented US Health System. JAMA. https://doi.org/10.1001/jama.2025.15488
Keywords: Health insurance, Children, Adolescents, Young people, Infants, Health care policy
