Weekly US Influenza Surveillance Report: Key Updates for Week 49, ending December 6, 2025 | FluView

U.S. influenza activity increased in Week 49 (week ending Dec. 6, 2025): clinical labs reported 4,790 positives (8.1% of 59,364 specimens) and ILINet ILI visits rose to 3.2%, exceeding the national baseline for the first time this season; ED influenza diagnoses and hospital admissions also increased. Influenza A(H3N2) is dominant (≈86% of subtyped viruses this week and 79% cumulatively) and antigenic testing shows most recent H3N2 viruses are poorly recognized by the current A(H3N2) vaccine reference (only ~9% well-recognized), raising vaccine‑effectiveness concerns, while A(H1N1)pdm09 and most B/Victoria viruses remain well-recognized. Hospitalizations are climbing (FluSurv‑NET weekly rate 2.2 per 100,000, up from 1.7; cumulative 6.9 per 100,000 — the third highest Week‑49 cumulative rate since 2010‑11), with highest burden in adults ≥65; antivirals (oseltamivir/zanamivir/peramivir/baloxavir) show retained activity and no new human H5 cases were reported. Two influenza‑associated pediatric deaths were reported and CDC surveillance data remain preliminary.

Analysis

CDC surveillance for Week 49 (week ending Dec. 6, 2025) shows rising U.S. influenza activity: clinical laboratories reported 4,790 positive specimens (8.1% of 59,364 tested) and ILINet visits for influenza‑like illness rose to 3.2%, exceeding the national baseline for the first week this season; NSSP ED influenza diagnoses (1.6%) and NHSN hospital admissions also increased, with Region 8 recording the highest laboratory percent positivity at 20.8%.

Virologic data are dominated by influenza A(H3N2) — ~86% of subtyped viruses this week and 79% cumulatively — and antigenic characterization indicates notable H3N2 drift: only ~9% of recent H3N2 isolates were well‑recognized by the 2025–26 A(H3N2) vaccine reference, whereas A(H1N1)pdm09 (23/23) and most B/Victoria viruses were well‑recognized. Antiviral susceptibility testing through the neuraminidase inhibitors and baloxavir showed no reduced inhibition in viruses tested, preserving therapeutic options.

Hospital burden is increasing: FluSurv‑NET weekly hospitalization rate rose to 2.2 per 100,000 (from 1.7) with a cumulative 6.9 per 100,000 — the third highest Week‑49 cumulative rate since 2010–11 — and highest rates among adults ≥65 (19.6 per 100,000) and children 0–4 (9.7). Reported racial/ethnic disparities in hospitalization rates and the preliminary nature of the data suggest continued volatility and regional heterogeneity to monitor closely.

Key Decisions for Investors

• Monitor weekly CDC virologic, antigenic and hospitalization releases (focus on regional signals such as Region 8 and hospital admission rates) and use sequential weekly updates to trigger tactical portfolio shifts
• Tilt exposure toward providers of antivirals, diagnostics/testing capacity and hospital services in the near term because antiviral susceptibility remains intact and hospitalizations are rising, but size positions conservatively given H3N2 vaccine‑recognition uncertainty
• Limit exposure to travel, leisure, and consumer discretionary names in markets tied to regions with rising ILINet/hospitalization metrics and consider short‑dated hedges if trends accelerate over the next 1–2 weeks
• Monitor pediatric and elderly hospitalization trends and long‑term care metrics for potential operational stress on hospital and LTC operators and prioritize investments in healthcare names with diversified revenue and strong balance sheets