When will CDC publish a U.S. vaccine effectiveness estimate for the 2025–26 season and how are those studies designed?
Executive summary
Public reporting from CDC and partner networks indicates there is no single fixed calendar date for a U.S. influenza vaccine effectiveness (VE) estimate for the 2025–26 season; instead CDC and its surveillance partners publish interim VE estimates as data accrue during the respiratory season (typically beginning once substantial circulation occurs in winter) and then publish final season summaries after the season ends (sources show interim Southern Hemisphere and U.S. network reports and CDC VE pages) [1] [2] [3]. Those U.S. estimates are generated using test‑negative case‑control designs with RT‑PCR confirmation, vaccination ascertainment from registries/EHR/self‑report, and multivariable logistic regression to produce (1 − adjusted odds ratio) × 100% VE estimates — the standard methods CDC public materials and MMWR reports describe [1] [4] [5] [2].
1. When U.S. VE estimates appear: timing is rolling, not a single release date
CDC and partner surveillance networks routinely issue interim VE estimates during the season as sentinel sites and electronic health record networks accumulate enough tested cases and controls; examples include MMWR and network reports that produce mid‑season estimates and later, end‑of‑season summaries, and CDC’s flu‑VE webpages that carry preliminary and final season charts [3] [6] [2]. There is no document in the provided reporting that sets a fixed future publication date for a 2025–26 U.S. VE estimate; instead historical practice and the CDC’s own Southern Hemisphere report show VE outputs are released when data are sufficient — usually once community circulation produces measurable numbers (Southern Hemisphere interim estimates were published after March–September surveillance) [1] [2].
2. How CDC and partners design VE studies: the test‑negative case‑control backbone
CDC’s influenza VE work uses the test‑negative case‑control design: patients seeking care for influenza‑like illness (ILI) or severe acute respiratory infection (SARI) who are eligible per national vaccination policy are tested by RT‑PCR; those testing positive are cases and those testing negative are controls [1]. Vaccination status is ascertained from national registries, medical records, or self‑report and vaccination is counted if given ≥14 days before symptom onset [1]. Analyses adjust for confounders using multivariable logistic regression and calculate VE as (1 − adjusted odds ratio) × 100%, a method CDC uses across respiratory‑virus VE programs including COVID‑19 examples from the VISION and IVY networks [4] [5] [3].
3. Data sources, networks, and outcomes that feed U.S. VE estimates
U.S. VE estimates come from a mix of sentinel outpatient and inpatient surveillance, multisite electronic health record‑based networks, and laboratory testing streams; CDC’s materials and MMWR papers reference ILI and SARI sentinel networks, the VISION and IVY networks for hospitalization and ED/UC outcomes, and linkage to vaccination registries or EHRs for exposure data [1] [7] [3]. Outcomes vary by study and can include medically attended outpatient visits, emergency department/urgent care encounters, and hospitalizations; CDC notes VE estimates differ across designs, outcomes, and populations studied [2].
4. Interpreting timing and results: Southern Hemisphere signals, mid‑season caveats, and competing interests
CDC has highlighted that Southern Hemisphere VE data can foreshadow Northern Hemisphere protection when vaccine composition is the same, but those data are explicitly conditional on similar circulating viruses — a caveat the MMWR Southern Hemisphere report stresses [1]. Interim U.S. VE reports are therefore provisional and subject to revision as more data accumulate; CDC’s VE webpages and MMWR practice show preliminary labels and varying confidence intervals across age and risk groups [2] [3]. Independent reviewers have warned that disruptions in advisory processes and varying data streams mean end users should weigh interim findings cautiously and consider multiple analyses (NEJM perspective) [8]. Finally, industry and advocacy citations of preliminary VE figures (for example company summaries referencing CDC burden or registry studies) underscore a need to note potential conflicts or selective emphasis when interpreting headline VE numbers [9].
5. Bottom line for the 2025–26 season
No single pre‑announced publication date for a 2025–26 U.S. VE estimate is present in the supplied reporting; expect CDC to publish rolling interim U.S. estimates once winter circulation yields adequate sample sizes — following the same test‑negative, RT‑PCR‑confirmed, registry/EHR‑linked analytic approach described in CDC and MMWR materials — with final season summaries posted after the season concludes [1] [4] [5] [2] [3]. The Southern Hemisphere interim report offers early context when vaccine composition matches, but CDC cautions about extrapolating directly unless circulating strains align [1].