Flu cases are on the rise in the US. Here's what you need to know

Influenza activity in the U.S. is ramping up: weekly test positivity reached 8.1% for the week ending Dec. 6 (roughly four times the 1.6% rate a month earlier), with more than 6,800 hospital admissions and the first pediatric death reported. Several states including New York (≈24,000 cases and ~1,400 hospitalizations that week versus ~12,000 cases and 850 hospitalizations last year) are seeing high ILI levels, and the H3N2 subclade K — accounting for 89% of genetically characterized samples since Sept. 28 — may better evade immunity. UK preprint data indicate the 2025–26 vaccine is 70–75% effective at preventing hospitalization in children and 30–40% in adults; public-health guidance continues to prioritize vaccination and antivirals where appropriate, which could temper severe-case risk but仍 poses downside to near-term consumer activity and travel.

Analysis

Market structure: Winners in a ramping flu season are vaccine manufacturers (Sanofi SNY, GSK GSK, Pfizer PFE) and diagnostics/rapid-test suppliers (Quidel QDEL, Abbott ABT) who see near-term volume and pricing power; hospital suppliers and smaller antivirals makers could also see demand but with mixed margin impact. Losers are travel & leisure (airlines AAL/DAL/UAL, cruise CCL) and discretionary retail tied to travel because even a 5–10% weekly increase in positivity can reduce booking rates and raise cancellation risk for 4–8 weeks. On supply/demand, rapid-test inventories are likely to tighten near-term—implying higher gross margins for diagnostic firms—while vaccine production is fixed for the season, capping upside for incumbent producers.

Risk assessment: Tail risks include a subclade K mutation that materially increases severity (low probability, high impact) or a mid-season vaccine composition change/regulatory action (material operational disruption). Time horizons: immediate (days) = travel/consumer flows and option vol spikes; short-term (weeks–months) = vaccine uptake, hospital admissions, antiviral prescriptions through Feb–Mar; long-term (quarters) = mRNA flu vaccine adoption (MRNA) and durable shifts in testing behavior. Hidden dependencies include concurrent RSV/COVID waves, insurer reimbursement dynamics, and school closure policies; key catalysts are CDC weekly positivity, pediatric mortality counts, and U.K./Japan VE data releases.

Trade implications: Direct plays — establish tactical longs in SNY/GSK (2–3% each) and QDEL/ABT (1–2%) to capture vaccine/test demand into Mar 2026, financed by reducing cyclicals. Use pair trade long SNY / short JETS (U.S. Global Jets ETF) to express defensive vs travel pain. Options: buy 3-month 25–30 delta puts on JETS (size 0.5–1% portfolio risk) or airline single-stock put spreads; buy 6–9 month call spreads on MRNA to play mRNA flu upside with defined risk. Rotate sector exposure into XLV/XLP and increase cash/T-bills if CDC national percent-positive >10%.

Contrarian angles: Consensus focuses on vaccines; market may be underpricing antiviral and diagnostics upside—if pediatric hospitalizations rise >20% WoW, antiviral scripts and rapid-test replacement cycles can outpace vaccine revenue growth by 2–3x in the short run. Historical parallel: H3N2-dominated seasons (e.g., 2017–18) produced 2–3 quarters of elevated diagnostics/antiviral sales, not permanent growth—so favor short-duration trades. Unintended consequence: aggressive public health measures (school closures, travel advisories) would amplify travel downside but cap medical sector stress; set re-eval triggers at CDC positivity <4% or hospitalizations down 30% WoW to exit defensives.

Key Decisions for Investors

• Establish a 2–3% long position in Sanofi (SNY) and GSK (GSK) split evenly now through March 2026 to capture higher seasonal vaccine uptake; trim by 50% if CDC national percent-positive for influenza falls below 4% for two consecutive weeks.
• Allocate 1–2% to diagnostics exposure via Quidel (QDEL) or Abbott (ABT) using outright longs or 3-month call spreads (buy 6-month calls, sell 3-month OTM calls) to exploit tightened rapid-test demand; reduce if inventory restocking announcements indicate >20% supply increase.
• Deploy a defensive pair: go long SNY (1.5%) and short JETS ETF (1.5%) or sell 1–2% notional exposure via JETS 3-month 25–delta put purchases (cost-risk ~0.5–1% portfolio) to profit from travel weakness during peak season; cover/flip if weekly airline bookings recover to pre-December baseline for two weeks.
• Buy 6–9 month call spreads on Moderna (MRNA) sized 0.5–1% to play mRNA flu vaccine adoption (defined-risk bullish); cap loss at premium paid and reassess on Q1 2026 trial/data updates.
• Increase cash/T-bill allocation by 3–5% as a tactical hedge if CDC reports national weekly hospitalizations rising >15% WoW or pediatric flu deaths exceed 3 in a single week; redeploy after two consecutive weeks of hospitalization decline ≥20%.