Avidity Biosciences (RNA) 8-KRegulation FD Disclosure

On March 4, 2024, Avidity Biosciences, Inc. (“Avidity” or the “Company”) will host an investor and analyst event (the "Event") to discuss new delpacibart etedesiran ("del-desiran") data from the MARINA-OLE™ trial of people living with myotonic dystrophy type 1 ("DM1"). Delpacibart etedesiran is the approved international nonproprietary name of AOC 1001. The Event will begin at 8:00 a.m. Eastern Time and will be available via a live video webcast accessible under the “Events and Presentations” page in the “Investors” section of Avidity’s corporate website, at https://www.aviditybiosciences.com. During the Event, the Company will present the corporate slide presentation attached as Exhibit 99.1 to this Current Report on Form 8-K, which is incorporated herein by reference.

The Company plans to initiate its Phase 3 HARBOR™ trial of del-desiran in the second quarter of 2024. The Key Endpoints are the same endpoints that will be used in the Phase 3 HARBOR trial of del-desiran.

Avidity cautions readers that statements contained in this Current Report on Form 8-K regarding matters that are not historical facts are forward-looking statements. These statements are based on the Company's current beliefs and expectations. Such forward-looking statements include, but are not limited to, statements regarding: the characterization of safety, tolerability and long-term efficacy data associated with del-desiran from the MARINA-OLE™ study; the impact of such data on the advancement of del-desiran; and a Phase 3 trial for del-desiran, the timing of its initiation and key endpoints to be used therein. This Current Report on Form 8-K also contains estimates and other statistical data made by independent parties and by us. This data involves a number of assumptions and limitations, and the reader is cautioned not to give undue weight to such estimates. The inclusion of forward-looking statements should not be regarded as a representation by Avidity that any of these plans will be achieved. Actual results may differ from those set forth in this Current Report on Form 8-K due to the risks and uncertainties inherent in Avidity's business, including, without limitation: Avidity may not be able to resolve the partial clinical hold related to the serious adverse event which occurred in the Phase 1/2 MARINA trial, which may result in delays in the clinical development of del-desiran; additional participant data related to del-desiran that continues to become available may be inconsistent with the data produced as of the date hereof, and further analysis of existing data and analysis of new data may lead to conclusions different from those established as of the date hereof; unexpected adverse side effects to, or inadequate efficacy of, Avidity's product candidates that may delay or limit their development, regulatory approval and/or commercialization, or may result in additional clinical holds which may not be timely lifted, recalls or product liability claims; Avidity is early in its development efforts; Avidity's approach to the discovery and development of product candidates based on its AOC platform is unproven, and the Company does not know whether it will be able to develop any products of commercial value; potential delays in the commencement, enrollment, data readouts and completion of preclinical studies or clinical trials; Avidity's dependence on third parties in connection with preclinical and clinical testing and product manufacturing; regulatory developments in the United States and foreign countries; and other risks described in Avidity's Annual Report on Form 10-K for the fiscal year ended December 31, 2023, filed with the Securities and Exchange Commission (SEC) on February 28, 2024, and in subsequent filings with the SEC. Avidity cautions readers not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and the Company undertakes no obligation to update such statements to reflect events that occur or circumstances that arise after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.