SION: 1Q26: CF PoC Readout On Track For Summer

Research evidence excerpt

SION: 1Q26: CF PoC Readout On Track For Summer

RBC Capital Markets, LLC

Brian Abrahams, M.D. (Head of Global Healthcare Research)

(212) 858-7066, brian.abrahams@rbc.com

Nevin Varghese, Ph.D. (Analyst)

(212) 301-1609, nevin.varghese@rbccm.com

Kevin Meli, Ph.D. (Senior Associate)

(212) 548-3110, kevin.meli@rbccm.com

May 12, 2026

Sionna Therapeutics Inc. Underperform

Speculative RiskRESEARCH 1Q26: CF PoC Readout On Track For Summer NASDAQ: SION; USD 45.95

Our view: Timelines for the highly-anticipated '719+SoC CF readout is on Price Target USD 23.00 ↓ 24.00

track for summer-'26, and investor inbounds continue to be high into the Scenario Analysis* data. We acknowledge that the upside could be meaningful if SION can

get either '719 or their proprietary dual combinations over the line, but Downside Price Current Upside

we still believe that SwCl benefits shown in the upcoming ph.IIa would Scenario Target Price Scenario

likely need to be convincingly higher than the company's 10mMol bar to 5.00 23.00 45.95 50.00

de-risk a pivotal program where functional benefits would be the likely 89% 50% 9%EQUITY

registrational endpoint, and remain cautious on this potential given the *Implied Total Returns

history of poor HBE assay translatability. A >$2B valuation predicated Key Statistics

on preclinical data from a historically unreliable assay and uncertainties Shares O/S (MM): 44,117.0 Market Cap (MM): 2,027,176 Dividend: 0.00 Yield: 0.0%

around biomarker to function translatability-- even acknowledging a large Avg. Daily Volume: 445,095

CF space and their novel mechanism-- still seems quite optimistic to us,

keeping us Underperform into the data. PT to $23 on model adjustments. RBC Estimates

FY Dec 2025A 2026E 2027E 2028E