When will the CDC publish U.S.-specific vaccine effectiveness estimates for the 2025–26 season?
Executive summary
The Centers for Disease Control and Prevention (CDC) does not publish a fixed calendar date for U.S.-specific influenza vaccine effectiveness (VE) estimates for a given season; instead, CDC’s four U.S. VE networks collect and analyze real‑world data and issue interim estimates once sufficient cases accumulate, with prior interim U.S. VE reports appearing in late winter (for example, an interim 2024–25 MMWR was published February 27, 2025) [1]. CDC pages for VE studies and FluView explain that early-season international and domestic surveillance inform expectations, while the agency’s VE networks continue collecting data through the season to produce preliminary and final estimates [2] [3] [4].
1. How CDC produces and times U.S. VE estimates — process, not a calendar
CDC’s approach hinges on multiple U.S. networks (IVY, US Flu VE, VISION, NVSN) that use test‑negative designs and pooled analyses to produce adjusted VE estimates when there are enough test‑positive and test‑negative cases to reach statistical reliability; CDC published interim U.S. VE estimates for the 2024–25 season as an MMWR in late February 2025 after networks analyzed data collected from October through February [1] [5]. The agency’s public materials and FluView weekly reports state that networks are “collecting real‑world data to produce early estimates of vaccine effectiveness in the United States” and that timing depends on sufficient virus circulation and reporting lags in surveillance systems [3] [4].
2. What to expect for 2025–26 timing based on past practice and current signals
By precedent and CDC practice, preliminary/interim U.S. VE estimates are typically released in late winter to early spring once the VE networks have accrued enough cases and completed adjusted analyses — a pattern illustrated by the February 27, 2025 MMWR interim report for 2024–25 and by CDC’s VE webpages that compile season estimates once analyses are complete [1] [2]. International mid‑season VE reports, such as Southern Hemisphere interim estimates published in September 2025, are used as early signals but do not replace U.S. analyses; CDC explicitly notes Southern Hemisphere VE can “help to prepare Northern Hemisphere health authorities” but cautions that U.S. estimates require domestic network data [6].
3. Why publication might come earlier or later this season — data flow and surveillance realities
Several operational factors can shift the timing: how rapidly influenza circulates in the U.S., laboratory confirmation and viral characterization throughput, reporting lags in hospital and outpatient networks, and the need to adjust for confounders in multivariable models (the same kinds of lags CDC documents in other vaccine surveillance work) [7] [1]. CDC’s weekly FluView and qualitative season outlooks confirm the agency is monitoring uptake and circulation in real time and that the VE networks will publish “early” estimates when statistically robust—meaning if circulation is intense early, interim estimates could appear on the earlier side of the late‑winter window; if circulation is sparse or data are delayed, publication will shift later [3] [4].
4. Bottom line and reporting caveats
The most accurate expectation, grounded in CDC’s published practice and the 2024–25 timeline, is that U.S.‑specific interim VE estimates for the 2025–26 season will appear in late winter to early spring (roughly February–March) after CDC’s VE networks complete their analyses, with final season summaries published later once full‑season data are available [1] [2]. Sources note international interim findings (e.g., Southern Hemisphere reports and UK mid‑season data) can provide early context and are already being cited by CDC and others, but those do not substitute for U.S. network estimates [6] [4]. The available reporting does not specify an exact calendar date for the 2025–26 U.S. VE release, so this timing is an evidence‑based projection rooted in CDC’s recent publication patterns and stated surveillance processes [2] [1].