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Background: Implementation research generally assumes established evidence-based practices and prior piloting of implementation strategies, which may not be feasible during a public health emergency. We describe the use of a simulation model of the effectiveness of COVID-19 mitigation strategies to inform a stakeholder-engaged process of rapidly designing a tailored intervention and implementation strategy for individuals with serious mental illness (SMI) and intellectual/developmental disabilities (ID/DD) in group homes in a hybrid effectiveness-implementation randomized trial. Methods: We used a validated dynamic microsimulation model of COVID-19 transmission and disease in late 2020/early 2021 to determine the most effective strategies to mitigate infections among Massachusetts group home staff and residents. Model inputs were informed by data from stakeholders, public records, and published literature. We assessed different prevention strategies, iterated over time with input from multidisciplinary stakeholders and pandemic evolution, including varying symptom screening, testing frequency, isolation, contact-time, use of personal protective equipment, and vaccination. Model outcomes included new infections in group home residents, new infections in group home staff, and resident hospital days. Sensitivity analyses were performed to account for parameter uncertainty. Results of the simulations informed a stakeholder-engaged process to select components of a tailored best practice intervention and implementation strategy. Results: The largest projected decrease in infections was with initial vaccination, with minimal benefit for additional routine testing. The initial level of actual vaccination in the group homes was estimated to reduce resident infections by 72.4% and staff infections by 55.9% over the 90-day time horizon. Increasing resident and staff vaccination uptake to a target goal of 90% further decreased resident infections by 45.2% and staff infections by 51.3%. Subsequent simulated removal of masking led to a 6.5% increase in infections among residents and 3.2% among staff. The simulation model results were presented to multidisciplinary stakeholders and policymakers to inform the "Tailored Best Practice" package for the hybrid effectiveness-implementation trial. Conclusions: Vaccination and decreasing vaccine hesitancy among staff were predicted to have the greatest impact in mitigating COVID-19 risk in vulnerable populations of group home residents and staff. Simulation modeling was effective in rapidly informing the selection of the prevention and implementation strategy in a hybrid effectiveness-implementation trial. Future implementation may benefit from this approach when rapid deployment is necessary in the absence of data on tailored interventions. Trial registration: ClinicalTrials.gov NCT04726371 [ABSTRACT FROM AUTHOR]

Background Individuals with psychotic symptoms experience substantial morbidity and have shortened life expectancies; early treatment may mitigate the worst effects. Understanding care preceding a first psychotic disorder diagnosis is critical to inform early detection and intervention. Study Design In this observational cohort study using comprehensive information from the Massachusetts All-Payer Claims Database, we identified the first psychotic disorder diagnosis in 2016, excluding those with historical psychotic disorder diagnoses in the prior 48 months among those continuous enrollment data. We reviewed visits, medications, and hospitalizations 2012–2016. We used logistic regression to examine characteristics associated with pre-diagnosis antipsychotic use. Study Results There were 2505 individuals aged 15–35 years (146 per 100 000 similarly aged individuals in the database) with a new psychotic disorder diagnosis in 2016. Most (97%) had at least one outpatient visit in the preceding 48 months; 89% had a prior mental health diagnosis unrelated to psychosis (eg, anxiety [60%], depression [60%]). Many received psychotropic medications (77%), including antipsychotic medications (46%), and 68% had a visit for injury or trauma during the preceding 48 months. Characteristics associated with filling an antipsychotic medication before the psychotic disorder diagnosis included male sex and Medicaid insurance at psychosis diagnosis. Conclusions In this insured population of Massachusetts residents with a new psychotic disorder diagnosis, nearly all had some healthcare utilization, visits for injury or trauma were common, and nearly half filled an antipsychotic medication in the preceding 48 months. These patterns of care could represent either pre-disease signals, delays, or both in receiving a formal diagnosis. [ABSTRACT FROM AUTHOR]

This study examined COVID-19 infection and hospitalizations among people with serious mental illness who resided in residential care group homes in Massachusetts during the first year of the COVID-19 pandemic. The authors analyzed data on 2261 group home residents and COVID-19 data from the Massachusetts Department of Public Health. Outcomes included positive COVID-19 tests and COVID-19 hospitalizations March 1, 2020–June 30, 2020 (wave 1) and July 1, 2020–March 31, 2021 (wave 2). Associations between hazard of outcomes and resident and group home characteristics were estimated using multi-level Cox frailty models including home- and city-level frailties. Between March 2020 and March 2021, 182 (8%) residents tested positive for COVID-19, and 51 (2%) had a COVID-19 hospitalization. Compared with the Massachusetts population, group home residents had age-adjusted rate ratios of 3.0 (4.86 vs. 1.60 per 100) for COVID infection and 13.5 (1.99 vs. 0.15 per 100) for COVID hospitalizations during wave 1; during wave 2, the rate ratios were 0.5 (4.55 vs. 8.48 per 100) and 1.7 (0.69 vs. 0.40 per 100). In Cox models, residents in homes with more beds, higher staff-to-resident ratios, recent infections among staff and other residents, and in cities with high community transmission risk had greater hazard of COVID-19 infection. Policies and interventions that target group home-specific risks are needed to mitigate adverse communicable disease outcomes in this population. Clinical Trial Registration Number This study provides baseline (i.e., pre-randomization) data from a clinical trial study NCT04726371. [ABSTRACT FROM AUTHOR]

Smoke-free policies (SFP) in multi-unit housing are a promising tool for reducing exposure to tobacco smoke among residents. Concerns about increased housing instability due to voluntary or involuntary transitions induced by SFPs have been a primary barrier to greater widespread adoption. The impact of SFP implementation on transitions out of public housing in federally funded public housing authorities in Massachusetts was evaluated. Tenancy data from the Department of Housing and Urban Development were used to determine the time from admission to transitioning out of public housing based on a cohort study design. Periods of exposure to SFPs were defined based on dates of SFP implementation at each PHA. Multi-level Cox regression models were fit to estimate the effects of SFPs on the hazard of transitioning, adjusting for household- and PHA-level characteristics. Analyses were conducted in 2021‒2022. There were 44,705 households with a record of residence in Massachusetts PHAs over 2009‒2018. Over this period, despite increasing adoption of SFPs among the PHAs, rates of transition remained steady at around 5‒8 transitions per 1,000 household-months. There was no overall association between exposure to SFPs and transitions among the full sample (adjusted HR=0.99, 95% CI=0.95, 1.04, p =0.794). However, the association varied significantly by age group, race/ethnicity, timing of SFP adoption, and era of admission. Adoption of SFPs in public housing had a minimal overall impact on turnover for households in Massachusetts, though disparities in the impact were observed between different demographic and PHA-level subgroups. [ABSTRACT FROM AUTHOR]

Importance: Federally qualified health centers (FQHCs) receive federal funding to serve medically underserved areas and provide a range of services including comprehensive primary care, enabling services, and behavioral health care. Greater funding for FQHCs could increase the local availability of clinic-based care and help reduce more costly resource use, such as emergency department visits (ED). Objective: To examine the impact of funding increases for FQHCs after the ACA on the use of FQHCs and EDs. Methods: Retrospective study using the Massachusetts All Payer Claims Database (APCD) 2010–2013 that included APCD enrollees in 559 Massachusetts ZIP codes (N = 6,173,563 in 2010). We calculated shift-share predictions of changes in FQHC funding at the ZIP code-level for FQHCs that received Community Health Center funds in any year, 2010–13 (N = 31). Outcomes were the number of ZIP code enrollees with visits to FQHCs and EDs, overall and for emergent and non-emergent diagnoses. Results: In 2010, 4% of study subjects visited a FQHC, and they were more likely to be younger, have Medicaid, and live in low-income areas. We found that a standard deviation increase in prior year FQHC funding (+31 percentage point (pp)) at the ZIP code level was associated with a 2.3pp (95% CI 0.7pp to 3.8pp) increase in enrollees with FQHC visits and a 1.3pp (95% CI -2.3pp to -0.3pp) decrease in enrollees with non-emergent ED visits, but no significant change in emergent ED visits (0.3pp, 95% CI -0.8pp to 1.4pp). Conclusions: We found that areas exposed to greater FQHC funding increases had more growth in the number of enrollees seen by FQHCs and greater reductions in ED visits for non-emergent conditions. Investment in FQHCs could be a promising approach to increase access to care for underserved populations and reduce costly ED visits, especially for primary care treatable or non-emergent conditions. [ABSTRACT FROM AUTHOR]

Objective: Access to specialty mental health care may be poor because many psychiatrists do not accept health insurance reimbursement, whereas many patients rely on insurance to help pay for care. The objective of this study was to examine the extent of participation in private insurance by licensed psychiatrists.Methods: Using 2013 Massachusetts licensing data and the All-Payer Claims Database (APCD), the authors performed a cross-sectional analysis of licensed psychiatrists in Massachusetts. The fraction of psychiatrists who filed insurance claims, number of unique patients with insurance claims per psychiatrist, and physician characteristics associated with insurance participation were evaluated.Results: In 2013, Massachusetts had 2,348 licensed psychiatrists. Overall, 79% (N=1,843) had at least one paid claim for an outpatient visit in the APCD, but only 6% (N=151) had claims for at least 300 patients per year (a full caseload). Psychiatrists had a median of 18 patients with claims (mean=73). Compared with psychiatrists 30-39 years since medical school graduation, those within 19 years since graduation were less likely to bill for an outpatient (7-19 years, odds ratio [OR]=0.67, 95% confidence interval [CI]=0.47-0.94) and less likely to have claims for ≥300 patients per year (7-19 years, OR=0.49, 95% CI=0.29-0.83). Participation varied across insurance types (93% for group commercial plans versus 33% for Medicaid managed care plans).Conclusions: Among Massachusetts psychiatrists, participation in the private insurance market appears to be limited. Older psychiatrists are more likely to participate, and patients' access to psychiatrists who accept insurance could worsen as these psychiatrists retire. [ABSTRACT FROM AUTHOR]

Research Objective: The Affordable Care Act (ACA) expanded coverage for young adults by allowing them to remain dependents on their parents' plans until age 26 (in 2010) and expanding Medicaid to childless adults with incomes <138% of the federal poverty level (FPL) (in 2014). However, even post‐ACA, uninsured rates by age group were highest among young adults. In 2014, Massachusetts also expanded Medicaid eligibility for children to 19‐20‐year‐olds with incomes up to 150% FPL, which could reduce potential gaps in coverage for those who would otherwise age out of eligibility for Medicaid as children after age 18. We used the Massachusetts All Payer Claims Database to examine changes in coverage for Medicaid enrollees who turned 19 years old before and after the policy change. Study Design: We used data from the Massachusetts All Payer Claims Database (MA‐APCD) from 2012–2016 to examine two cohorts: Medicaid enrollees age 18 as of January 2012 and as of January 2014, who turned 19 years old prior to vs. after Medicaid expansion (pre‐ and post‐expansion cohorts, respectively). Monthly coverage changes for each cohort were examined for 2 years until they turned 21 years old (2012–2014 or 2014–2016). We classified months without insurance enrollment records as uninsured. We used logistic regression models to compare the likelihood of being uninsured for 3 or more months at age 19–20 and 20–21 for the pre‐ vs. post‐expansion cohorts, adjusting for gender, diagnoses of asthma, autism, obesity, mental illness, and intellectual and development disabilities, and ZIP code socioeconomic status (SES). Population Studied: Medicaid enrollees age 18 in January 2012 (N = 32,832) and January 2014 (N = 31,894) in the MA‐APCD. Principal Findings: In both cohorts, 49% were female and 29% lived in low SES ZIP codes; those who turned 19 prior to vs. after Medicaid expansion were less likely to have a baseline diagnosis of asthma (12.1% vs. 12.9%, p < 0.05), obesity (7.6% vs. 8.7%, p < 0.05), and mental illness (17.4% vs. 18.8%, p < 0.05). Enrollees who turned 19 prior to vs. after Medicaid expansion were more likely to have ≥3 months of commercial insurance at age 19–20 (8.5% vs. 3.6%; OR = 1.85, 95% CI 1.7, 2.0) and ≥ 3 months without insurance (17.0% vs. 1.2%; OR = 20.3, 95% CI 17.4, 23.6). Differences persisted at age 20–21, although both cohorts had access to Medicaid expansion for low‐income adults in these years (7.6% vs. 4.9%, OR = 1.4, 95% CI 1.3,1.6 for ≥3 months of commercial insurance; 11.5% vs. 0.9%, OR = 16.4, 95% CI 13.7, 19.5 for ≥3 months without insurance). Conclusions: Disruptions in insurance coverage for young adults aging out of Medicaid were substantially reduced in Massachusetts after the state expanded Medicaid for children to cover 19–20‐year‐olds and expanded coverage for low‐income adults. Commercial insurance coverage was also less likely for young adults after Medicaid expansion. Medicaid enrollees that entered adulthood prior to vs. after Medicaid expansion were more likely to be uninsured in years after Medicaid expansion. Implications for Policy or Practice: Expanding Medicaid eligibility for children to those ages 19–20 could substantially reduce the risk of becoming uninsured for low‐income children entering young adulthood. Primary Funding Source: Agency for Healthcare Research and Quality. [ABSTRACT FROM AUTHOR]

Background: More than seven million people with intellectual and/or developmental disabilities (ID/DD) live in the US and may face an elevated risk for COVID-19., Objective: To identify correlates of COVID-19 and related hospitalizations among people with ID/DD in group homes in Massachusetts., Methods: We collected data during March 1, 2020-June 30, 2020 (wave 1) and July 1, 2020-March 31, 2021 (wave 2) from the Massachusetts Department of Public Health and six organizations administering 206 group homes for 1035 residents with ID/DD. The main outcomes were COVID-19 infections and related hospitalizations. We fit multilevel Cox proportional hazards models to estimate associations with observed predictors and assess contextual home- and organizational-level effects., Results: Compared with Massachusetts residents, group home residents had a higher age-adjusted rate of COVID-19 in wave 1 (incidence rate ratio [IRR], 12.06; 95 % confidence interval [CI], 10.51-13.84) and wave 2 (IRR, 2.47; 95 % CI, 2.12-2.88) and a higher age-adjusted rate of COVID-19 hospitalizations in wave 1 (IRR, 17.64; 95 % CI, 12.59-24.70) and wave 2 (IRR, 4.95; 95 % CI, 3.23-7.60). COVID-19 infections and hospitalizations were more likely among residents aged 65+ and in group homes with 6+ resident beds and recent infection among staff and residents., Conclusions: Aggressive efforts to decrease resident density, staff-to-resident ratios, and staff infections through efforts such as vaccination, in addition to ongoing access to personal protective equipment and COVID-19 testing, may reduce COVID-19 and related hospitalizations in people with ID/DD living in group homes., Competing Interests: Declaration of competing interest Dr. Levison is a medical advisor to eMED, LLC. Dr. Tsai receives a financial honorarium from Elsevier, Inc. for his work as Co-Editor in Chief of the Elsevier-owned journal SSM-Mental Health. Dr. Donelan is an unpaid board member of Bridges Associates Inc, a non-profit organization serving persons with intellectual and developmental disabilities. Dr. Becker is a current recipient of the American Academy of Child and Adolescent Psychiatry (AACAP) Junior Investigator Award supported by AACAP and Industry Sponsors (Sunovion Pharmaceuticals, Inc. and Supernus Pharmaceuticals, Inc.). Dr. Skotko occasionally consults on the topic of Down syndrome through Gerson Lehrman Group. He receives remuneration from Down syndrome non-profit organizations for speaking engagements and associated travel expenses. In the past two years, Dr. Skotko received annual royalties from Woodbine House, Inc., for the publication of his book, Fasten Your Seatbelt: A Crash Course on Down Syndrome for Brothers and Sisters. Within the past two years, he has received research funding from F. Hoffmann-La Roche, Inc., AC Immune, and LuMind Research Down Syndrome Foundation to conduct clinical trials for people with Down syndrome. Dr. Skotko is occasionally asked to serve as an expert witness for legal cases where Down syndrome is discussed. Dr. Skotko serves in a non-paid capacity on the Honorary Board of Directors for the Massachusetts Down Syndrome Congress and the Professional Advisory Committee for the National Center for Prenatal and Postnatal Down Syndrome Resources. Dr. Skotko has a sister with Down syndrome., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Federally Qualified Health Centers (FQHCs) are a critical source of care for medically underserved populations and often serve as medical homes for individuals with serious mental illness (SMI). Many FQHCs provide mental health services and could facilitate access to mental health treatment within and outside of FQHCs. This study compared mental health care utilization and acute care events for adult Medicaid enrollees with SMI who receive care at Federally Qualified Health Centers (FQHCs) vs. other settings., Methods: This study used the 2015-2016 Massachusetts All-Payer Claims Database to examine outpatient mental health care and acute care events for 32,330 Medicaid adults, ages 18-64 and with major depressive, bipolar, or schizophrenia spectrum disorders (SSD), who resided in FQHC service areas and received care from FQHCs vs. other settings in 2015. Multivariable linear regressions assessed associations between receiving care at FQHCs and outpatient mental health visits, psychotropic medication fills, and acute care events in 2016., Results: There were 8,887 (27.5%) adults in the study population (N = 32,330) who had at least one FQHC visit in 2015. Those who received care at FQHCs were more likely to have outpatient mental health visits (73.3% vs. 71.2%) and psychotropic medication fills (73.2% vs. 69.0%, both p < .05), including antidepressants among those with depressive disorders and antipsychotics among those with SSD. They were more likely to have ED visits (74.0% vs. 68.7%), but less likely to be hospitalized (27.8% vs. 31.9%, both p < .05). However, there was no significant difference in the likelihood of having an acute psychiatric hospitalization (9.5% vs. 9.8%, p = .35)., Conclusions: Among Medicaid enrollees with SMIs who had access to care at FQHCs, those receiving care at FQHCs were more likely to have outpatient mental health visits and psychotropic medication fills, with lower rates of hospitalization, suggesting potentially improved quality of outpatient care. Higher ED visit rates among those receiving care at FQHCs warrant additional investigation., (© 2024. The Author(s).)

Importance: Health systems are increasingly addressing health-related social needs. The Massachusetts Flexible Services program (Flex) is a 3-year pilot program to address food insecurity and housing insecurity by connecting Medicaid accountable care organization (ACO) enrollees to community resources., Objective: To understand barriers and facilitators of Flex implementation in 1 Medicaid ACO during the first 17 months of the program., Design, Setting, and Participants: This mixed-methods qualitative evaluation study from March 2020 to July 2021 used the Reach, Efficacy, Adoption, Implementation, Maintenance/Practical, Robust Implementation, and Sustainability Model (RE-AIM/PRISM) framework. Two Mass General Brigham (MGB) hospitals and affiliated community health centers were included in the analysis. Quantitative data included all MGB Medicaid ACO enrollees. Qualitative interviews were conducted with 15 members of ACO staff and 17 Flex enrollees., Main Outcomes and Measures: Reach was assessed by the proportion of ACO enrollees who completed annual social needs screening (eg, food insecurity and housing insecurity) and the proportion and demographics of Flex enrollees. Qualitative interviews examined other RE-AIM/PRISM constructs (eg, implementation challenges, facilitators, and perceived effectiveness)., Results: Of 67 098 Medicaid ACO enrollees from March 2020 to July 2021 (mean [SD] age, 28.8 [18.7] years), 38 442 (57.3%) completed at least 1 social needs screening; 10 730 (16.0%) screened positive for food insecurity, and 7401 (11.0%) screened positive for housing insecurity. There were 658 (1.6%) adults (mean [SD] age, 46.6 [11.8] years) and 173 (0.7%) children (<21 years; mean [SD] age, 10.1 [5.5]) enrolled in Flex; of these 831 people, 613 (73.8%) were female, 444 (53.4%) were Hispanic/Latinx, and 172 (20.7%) were Black. Most Flex enrollees (584 [88.8%] adults; 143 [82.7%] children) received the intended nutrition or housing services. Implementation challenges identified by staff interviewed included administrative burden, coordination with community organizations, data-sharing and information-sharing, and COVID-19 factors (eg, reduced clinical visits). Implementation facilitators included administrative funding for enrollment staff, bidirectional communication with community partners, adaptive strategies to identify eligible patients, and raising clinician awareness of Flex. In Flex enrollee interviews, those receiving nutrition services reported increased healthy eating and food security; they also reported higher program satisfaction than Flex enrollees receiving housing services. Enrollees who received nutrition services that allowed for selecting food based on preferences reported higher satisfaction than those not able to select food., Conclusions and Relevance: This mixed-methods qualitative evaluation study found that to improve implementation, Medicaid and health system programs that address social needs may benefit from providing funding for administrative costs, developing bidirectional data-sharing platforms, and tailoring support to patient preferences.

Background: Collaborative care models (CoCM) that integrate mental health and primary care improve outcomes and could help address racial and ethnic mental health disparities. We examined whether use of these programs differs by race/ethnicity., Methods: This retrospective study examined two CoCM interventions implemented across primary care clinics in a large health system in Massachusetts: 1) a primary care-based behavioral health program for depression or anxiety (IMPACT model) and 2) referral to community-based specialty care services (Resource-finding). Outcomes included enrollment, non-completion, and symptom screening rates, and discharge status for Black, Hispanic and White patients referred for CoCM, 2017-2019., Results: Black and Hispanic vs. White patients referred to CoCM (n = 17,280) were more likely to live in high poverty ZIP codes (34% and 40% vs. 9%). Rates of program enrollment, non-completion, and symptom screening were similar across groups (e.g., 76%, 77%, and 75% of Black, Hispanic, and White patients enrolled). Hispanic vs. White patients were more likely to be enrolled in IMPACT (56%) vs. Resource-finding (43%). Among those completing IMPACT, Hispanic vs. White patients were more likely to be stepped to psychiatry vs. discharged to their primary care provider (51% vs. 20%, aOR = 1.55, 95% CI: 1.02-2.35)., Conclusions: Black and Hispanic patients referred to CoCM were similarly likely to use the program as White patients. Hispanic patients completing IMPACT were more frequently referred to psychiatry., Implications: These results highlight the promise of CoCMs for engaging minority populations in mental healthcare. Hispanic patients may benefit from additional intervention or earlier linkage to specialty care., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dr. Kovachy: None. Dr. Chang: None. Dr. Vogeli: Grant support from the National Institute of Aging, and National Institute of Diabetes and Digestive and Kidney Diseases Suzanne Tolland: None Susan Garrels: None Dr. Forester: Grant support from National Institute of Aging, Rogers Family Foundation Spier Family Foundation, Biogen, and Lilly. Dr. Fung: Grant support from the National Institutes of Health, Agency for Healthcare Research and Quality; Holds equity in Vertex pharmaceuticals, (Copyright © 2023 Elsevier Inc. All rights reserved.)

A 2018 rule requiring federally-subsidized public housing authorities (PHAs) in the United States to adopt smoke-free policies (SFPs) has sparked interest in how housing agencies can best implement SFPs. However, to date, there is little quantitative data on the implementation of SFPs in public housing. Massachusetts PHAs were among the pioneers of SFPs in public housing, and many had instituted SFPs voluntarily prior to the federal rule. The aim of this study was to examine the adoption, implementation, and outcomes of SFPs instituted in Massachusetts PHAs prior to 2018 using a survey conducted that year. The survey asked if PHAs had SFPs and, if so, what activities were used to implement them: providing information sessions, offering treatment or referral for smoking cessation, soliciting resident input, training staff, partnering with outside groups, using a toolkit, and/or providing outdoor smoking areas. We used multivariable regression to investigate associations between implementation activities and respondent-reported policy outcomes (resident support, complaints about neighbors' smoking, and the number of violations reported per year). Of 238 Massachusetts PHAs, 218 (91%) completed the survey and 161 had an SFP prior to 2018. Common implementation activities were offering smoking cessation treatment/referral (89%) and information sessions for residents (85%). Information sessions for residents were associated with higher resident support (adjusted odds ratio [AOR] 4.3; 95%CI 1.2-15.3). Training staff (AOR 6.3, 95%CI 1.2-31.8) and engaging in ≥5 implementation activities (AOR 4.1, 95%CI 1.2-14.1) were associated with fewer smoking-related complaints. Utilization of multiple implementation activities, especially ones that informed residents and trained PHA staff, was associated with more favorable policy outcomes. We identified five groups of PHAs that shared distinct patterns of SFP implementation activities. Our findings, documenting implementation activities and their associations with SFP outcomes among the early adopters of SPFs in Massachusetts public housing, can help inform best practices for the future implementation of SFPs in multiunit housing.

Importance: Young adults historically have had the highest uninsured rates among all age groups. In 2014, in addition to Medicaid expansion for adults with low income (≤133% of the federal poverty level [FPL]) through the Patient Protection and Affordable Care Act, Massachusetts also extended eligibility for children (≤150% FPL) to beneficiaries aged 19 to 20 years., Objective: To examine changes in insurance coverage continuity for Medicaid enrollees who turned age 19 years before and after eligibility policy changes., Design Setting and Participants: This cohort study used data from the Massachusetts All-Payer Claims Database (2012 to 2016) to compare coverage for Medicaid beneficiaries turning age 19 years before and after Medicaid expansion. Monthly coverage was examined for each cohort for 3 years as beneficiaries aged from 18 and 19 years to 19 and 20 years to 20 and 21 years. Analyses were performed between November 1, 2020, and May 12, 2022., Main Outcomes and Measures: In each year, the likelihood of being uninsured or having Medicaid, employer-sponsored insurance, or individual commercial coverage for 3 or more months was examined along with the likelihood of having continuous Medicaid enrollment for 12 or more and 24 or more months. Multivariable linear probability models were used to compare the likelihood of these outcomes for those in the postexpansion vs preexpansion cohorts, adjusting for sex, comorbidity levels, neighborhood socioeconomic status, and neighborhood race and ethnicity., Results: A total of 41 247 young adults turning age 18 to 19 years in the baseline year (20 876 [50.6%] men) were included in the study, with 20 777 in the preexpansion cohort and 20 470 in the postexpansion cohort. Enrollees who turned age 19 years after vs before the Medicaid eligibility expansion were less likely to have 3 or more uninsured months at ages 18 to 19 years (4.4% [n = 891] vs 22.9% [n = 4750]; adjusted difference, -18.4 [95% CI, -19.0 to -17.7] percentage points) and 19 to 20 years (13.2% [n = 2702] vs 35.8% [n = 7447]; adjusted difference, -22.4 [95% CI, -23.2 to -21.6] percentage points) and more likely to have continuous insurance coverage for 12 or more months (94.1% [n = 19 272] vs 63.7% [n = 13 234]; adjusted difference, 30.5 [95% CI, 29.7-31.2] percentage points) or 24 or more months (77.5% [n = 15 868] vs 44.4% [n = 9221]; adjusted difference, 33.0 [95% CI, 32.1-33.9] percentage points). Differences in the likelihood of having 3 or more uninsured months diminished at ages 20 to 21 years, when both groups had access to Medicaid (ie, in calendar years 2014 for the preexpansion cohort and 2016 for the postexpansion cohort)., Conclusions and Relevance: In this cohort study of young adults in Massachusetts, the combination of expanding Medicaid to lower-income adults and increasing the age threshold for child Medicaid eligibility was associated with reduced likelihood of becoming uninsured among Medicaid enrollees entering adulthood., Competing Interests: Conflict of Interest Disclosures: Dr Fung reported receiving grants from the National Institutes of Health (NIH) and Agency for Healthcare Research and Quality (AHRQ) and personal fees from Ginger outside the submitted work. Dr Yang reported receiving grants from AHRQ during the conduct of the study. Dr Hsu reported receiving grants from the NIH and AHRQ during the conduct of the study and personal fees for consulting from Cambridge Health Alliance, AltaMed, Columbia University, University of Southern California, Delta Health Alliance, and Community Servings outside the submitted work. Dr Newhouse reported receiving grants from the National Institute of Aging and AHRQ during the conduct of the study. No other disclosures were reported., (Copyright 2022 Fung V et al. JAMA Health Forum.)