Company: SION
Filing Date: 2025-02-07
Form Type: S-8
Source: 0001193125-25-022767
Chunk: 6

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: S-8
Chunk 6
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 such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

SIGNATURES Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Waltham, Massachusetts, on this 7 thday of February, 2025.

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

POWER OF ATTORNEY AND SIGNATURES Each individual whose signature appears below hereby constitutes and appoints each of Michael Cloonan, M.B.A. and Elena Ridloff, C.F.A., as such person’s true and lawful attorney-in-factand agent with full power of substitution and resubstitution, for such person in such person’s name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement on Form S-8,and to file the same, with all exhibits thereto, and all documents in connection therewith, with the Securities and Exchange Commission granting unto each said attorney-in-factand agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as such person might or could do in person, hereby ratifying and confirming all that any said attorney-in-factand agent, or any substitute or substitutes of any of them, may lawfully do or cause to be done by virtue hereof. Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons 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, Chief Executive Officer and                         
 Director                                                       
 (Principal Executive Officer)                                  
 Chief Financial Officer and                                    
 Head of Corporate Development                                  
 (Principal Financial Officer and