Primary Care Cost Sharing in Medicare Advantage.

Importance: Medicare Advantage (MA) plans increasingly leverage cost-sharing structure to incentivize high-value care utilization, yet national adoption and distribution of $0 cost sharing for in-network primary care physician (PCP) visits remain poorly characterized. Objective: To examine longitudinal trends and plan- and county-level characteristics of $0 cost sharing for in-network PCP visits among MA plans. Design, Setting, and Participants: This cross-sectional study involved a retrospective ecological analysis of MA plan-county observations, including general enrollment MA plans (health maintenance organization, preferred provider organization, and health maintenance organization point-of-service plans) offered across US counties from 2019 to 2025. Data were analyzed from December 2025 to March 2026. Exposures: Plan-level characteristics (plan type, premium status, geographic region, and Centers for Medicare & Medicaid Services star rating) and county-level characteristics (MA penetration, urbanicity, federal poverty level, racial and ethnic composition, and PCP accessibility). Main Outcomes and Measures: The primary outcome was the enrollment trend in MA plans offering $0 cost sharing for in-network PCP visits from 2019 to 2025. Secondary outcomes included plan- and county-level factors associated with offering this benefit in 2025, estimated using multivariable mixed-effects logistic regression with county-level random intercepts. Results: The proportion of MA beneficiaries enrolled in plans requiring no cost sharing for in-network PCP visits increased from 46.4% in 2019 to 78.1% in 2025 (P for trend < .001), equating to approximately 15 million additional beneficiaries. In 2025, plans offering this benefit were more likely preferred provider organization plans than health maintenance organization plans (adjusted odds ratio [AOR], 2.14; 95% CI, 2.05-2.23) and featured better performances (5-star rating: AOR, 6.71; 95% CI, 4.83-9.32). Geographically, plans offering this benefit were more prevalent in urbanized counties (AOR, 1.17; 95% CI, 1.11-1.24), had higher MA penetration (AOR, 1.31; 95% CI, 1.22-1.40, and had larger proportions of racial and ethnic minority populations (AOR, 1.18; 95% CI, 1.09-1.28). In contrast, zero-premium plans (AOR, 0.70; 95% CI, 0.68-0.73) and plans offered in high-poverty counties (AOR, 0.82; 95% CI, 0.74-0.90) showed considerably lower availability of $0 cost sharing. Conclusions and Relevance: This cross-sectional study demonstrates that $0 cost sharing for PCP visits has expanded rapidly under MA but remains unevenly distributed. Lower availability in zero-premium plans and high-poverty areas suggest strategic trade-offs between premiums and point-of-service costs, raising equity concerns that underscore the need to assess whether market-driven benefit design optimizes and sustains high-value primary care access to counties at greater populational health risk.