Company: SION
Filing Date: 2025-02-06
Form Type: S-1MEF
Source: 0001193125-25-021938
Chunk: 2

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-06
Form: S-1MEF
Chunk 2
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 an Exhibit Index attached hereto and filed herewith. EXHIBIT INDEX

| Exhibit 
 No.     |     | Exhibit Index                                                                    |
| 5.1     |     | Opinion of Goodwin Procter LLP.                                                  |
| 23.1    |     | Consent of Deloitte & Touche LLP, independent registered public accounting firm. |
| 23.2    |     | Consent of Goodwin Procter LLP (included in Exhibit 5.1)                         |
| 24.1*   |     | Power of Attorney (included on signature page).                                  |
| 107     |     | Filing Fee Table                                                                 |

| * | Previously filed on the signature page to the Registrant’s Registration Statement on Form S-1, as amended (File No. 333-284352), originally filed with the Securities and Exchange Commission on January 17, 2025 and incorporated by reference herein. |

SIGNATURES Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant has duly caused this registration statement on Form S-1to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Waltham, Massachusetts, on the 6th day of February, 2025.

| SIONNA THERAPEUTICS, INC. |     |                                       |
| By:                       |     | /s/ Michael S. Cloonan                |
| Name:                     |     | Michael S. Cloonan                    |
| Title:                    |     | President and Chief Executive Officer |

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement on Form S-1has been signed by the following person in the capacities and on the date indicated.

| Name                    
 /s/ Michael Cloonan     
 Michael Cloonan, M.B.A. 
 /s/ Elena Ridloff       
 Elena Ridloff, C.F.A.   |     | Title                                                               
 President and Chief Executive Officer (Principal Executive Officer) 
 Chief Financial Officer and Head of Corporate Development           
 (Principal Financial Officer and                                    
 Principal Accounting Officer)                                       |     | Date             
 February 6, 2025 
 February 6, 2025 |
|:------------------------|:----|:--------------------------------------------------------------------|:----|:-----------------|
| * Paul Clancy,          
 M.B.A.                  |     | Chair of the Board of Directors                                     |     | February