Additional Proxy Soliciting Materials (Form DEFA14A)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant ☒

Filed by a party other than the Registrant ☐

Check the appropriate box:

AVIDITY BIOSCIENCES, INC.

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

This Schedule 14A relates solely to preliminary communications made prior to furnishing security holders of Avidity Biosciences, Inc. ("Avidity" or the "Company") with a proxy statement related to a proposed transaction in which Ajax Acquisition Sub, Inc. ("Merger Sub"), an indirect wholly owned subsidiary of Novartis AG ("Novartis" or "Parent"), will be merged with and into the Company, with the Company being the surviving corporation and continuing as an indirect wholly owned subsidiary of Parent (the "Merger"), upon the terms and subject to the conditions set forth in the Agreement and Plan of Merger, dated October 25, 2025, among the Company, Parent, and Merger Sub.

In connection with the Merger, the Company, Bryce Therapeutics, Inc. (which on December 8, 2025, changed its name to Atrium Therapeutics, Inc.), a Delaware corporation and wholly owned subsidiary of the Company ("SpinCo"), and Parent (with respect to certain sections specified therein) entered into a Separation and Distribution Agreement, dated October 25, 2025 (the "Separation and Distribution Agreement"), pursuant to which, on the terms and subject to the conditions set forth in the Separation and Distribution Agreement, prior to the effective time of the Merger (the "Effective Time"): (i) the Company will effect a pre-closing reorganization, which will result in SpinCo owning, assuming or retaining all assets and liabilities of the Company and its subsidiaries related to their early stage precision cardiology programs and certain collaboration agreements, and the Company owning, assuming or retaining all other assets and liabilities and (ii) thereafter, the Company will either (a) distribute to its stockholders as of the distribution record date, on a pro rata basis, all of the issued and outstanding shares of SpinCo Common Stock, par value $0.001 per share ("SpinCo Common Stock"), at a ratio of 1 share of SpinCo Common Stock per 10 shares of common stock, par value $0.0001 per share, of the Company, with SpinCo continuing its existence as a separate and independent company or (b) consummate a sale of SpinCo to a third party, subject to the terms and conditions specified in the Merger Agreement and the Separation and Distribution Agreement. Following completion of the transactions contemplated by the Separation and Distribution Agreement (the "Spin-Off"), the Company will have no continuing ownership interest in SpinCo. The Spin-Off also includes certain assets of the Company that trigger a right of first negotiation with an existing collaboration partner of the Company that was notified concurrently with the Company's announcement of its entry into the Merger Agreement.

This Schedule 14A filing consists of the following documents relating to the Merger, the Spin-Off and the other transactions contemplated by the Merger Agreement:

Exhibit 99.1:  End of Year Message from Novartis CEO

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Additional Information and Where to Find It

In connection with the Spin-Off and the Merger (the "Transactions"), Novartis, Avidity and SpinCo intend to file relevant documents with the SEC, including a definitive proxy statement to be filed by Avidity. The definitive proxy statement and proxy card will be delivered to the stockholders of Avidity in advance of the special meeting relating to the Transactions. This document is not a substitute for the proxy statement or any other document that may be filed by Avidity with the SEC. AVIDITY'S STOCKHOLDERS ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT IN ITS ENTIRETY WHEN IT BECOMES AVAILABLE AND ANY OTHER DOCUMENTS FILED BY EACH OF NOVARTIS AND AVIDITY WITH THE SEC IN CONNECTION WITH THE TRANSACTIONS OR INCORPORATED BY REFERENCE THEREIN BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTIONS AND THE PARTIES TO THE PROPOSED TRANSACTIONS. Investors and security holders will be able to obtain a free copy of the proxy statement and such other documents containing important information about Novartis and Avidity, once such documents are filed with the SEC, through the website maintained by the SEC at www.sec.gov. Novartis and Avidity make available free of charge at the Novartis website at www.novartis.com/investors/financial-data/sec-filings and Avidity's website at investors.aviditybiosciences.com/sec-filings, respectively, copies of documents they file with, or furnish to, the SEC. The contents of the websites referenced above will not be deemed to be incorporated by reference into the proxy statement.

Participants in the Solicitation

This communication does not constitute a solicitation of a proxy. Novartis, Avidity and their respective directors, executive officers and certain employees may be deemed to be participants in the solicitation of proxies from the stockholders of Avidity in connection with the Transactions. Information regarding the special interests of these directors and executive officers in the Transactions will be included in the definitive proxy statement referred to above. Security holders may also obtain information regarding the names, affiliations and interests of the Novartis directors and executive officers in the Novartis Annual Report on Form 20-F for the fiscal year ended December 31, 2024, which was filed with the SEC on January 31, 2025. Security holders may obtain information regarding the names, affiliations and interests of Avidity's directors and executive officers in Avidity's definitive proxy statement on Schedule 14A, which was filed with the SEC on April 29, 2025. To the extent the holdings of Avidity's securities by Avidity's directors and executive officers have changed since the amounts set forth in Avidity's definitive proxy statement for its 2025 annual meeting of stockholders, such changes have been or will be reflected on Initial Statements of Beneficial Ownership on Form 3 or Statements of Change in Ownership on Form 4 filed with the SEC. These documents (when available) may be obtained free of charge from the SEC's website at www.sec.gov, the Novartis website at www.novartis.com/investors/financial-data/sec-filings and Avidity's website at investors.aviditybiosciences.com/sec-filings. The contents of the websites referenced above are not deemed to be incorporated by reference into the proxy statement.

No Offer or Solicitation

This communication is for informational purposes only and is not intended to and does not constitute, or form part of, an offer, invitation or the solicitation of an offer or invitation to purchase, otherwise acquire, subscribe for, sell or otherwise dispose of any securities, or the solicitation of any vote or approval in any jurisdiction, pursuant to the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in contravention of applicable law.

Forward-Looking Statements

This communication contains forward-looking statements within the meaning of the United States Private Securities Litigation Reform Act of 1995. Forward-looking statements can generally be identified by words such as "potential," "can," "will," "plan," "may," "could," "would," "expect," "anticipate," "look forward," "believe," "committed," "investigational," "pipeline," "launch," or similar terms, or by express or implied discussions regarding the proposed acquisition of Avidity and Avidity's related Spin-Off, the expected timetable for completing each of the proposed Transactions, the composition of the assets and liabilities to be held by SpinCo and Avidity following the Spin-Off, the management team for SpinCo and its cash balance, potential marketing approvals, new indications or labeling for Avidity's product candidates, Avidity's platform and preclinical assets, or potential future revenues from Avidity's product candidates. You should not place undue reliance on these statements. Such forward-looking statements are based on our current beliefs and expectations regarding future events, and are subject to significant known and unknown risks and uncertainties. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those set forth in the forward-looking statements. There can be no guarantee that Avidity's investigational products will be submitted or approved for sale or for any additional indications or labeling in any market, or at any particular time, or that Avidity's approach to the discovery and development of product candidates based on its AOC^™ platform will produce any products of commercial value. There can be no guarantee that the conditions to the closing of the Transactions will be satisfied on the expected

timetable or at all or that the expected benefits or synergies from the Transactions will be achieved in the expected timeframe, or at all. In particular, expectations regarding Avidity, SpinCo, or the Transactions could be affected by, among other things, the timing of the satisfaction of customary closing conditions, including the receipt of regulatory approvals and the approval of Avidity's stockholders, on acceptable terms or at all; risks and costs related to the implementation of the separation of SpinCo, including the ability to complete the separation in the anticipated timeframe, or at all, and any changes to the configuration of the businesses included in the separation if implemented; the sale of certain of SpinCo's assets pursuant to a third party right of first negotiation; the risk that competing offers or acquisition proposals will be made; the effects of disruption from the Transactions and the impact of the announcement and pendency of the Transactions on Novartis' and/or Avidity's businesses, including their relationships with employees, business partners or governmental entities; the risk that the Transactions may be more expensive to complete than anticipated; the risk that stockholder litigation in connection with the Transactions may result in significant costs of defense, indemnification and liability; a diversion of management's attention from ongoing business operations and opportunities as a result of the Transactions or otherwise; the uncertainties inherent in research and development, including clinical trial results and additional analysis of existing clinical data; regulatory actions or delays or government regulation generally; and the risks and factors referred to in Novartis' most recent Annual Report on Form 20-F for the year ended December 31, 2024, Avidity's Annual Report on Form 10-K for the year ended December 31, 2024 and Quarterly Reports on Form 10-Q for the quarters ended March 31, 2025, June 30, 2025 and September 30, 2025, and any subsequent filings made by either party with the SEC, available on the SEC's website at www.sec.gov. Avidity is providing the information in this communication as of this date and does not undertake any obligation to update any forward-looking statements contained in this communication as a result of new information, future events or otherwise, except to the extent required by law.

Exhibit 99.1

End of Year Message from Novartis CEO

The Company shared the following letter from Vasant Narasimhan, CEO of Novartis, on its Basecamp site that is accessible to Company employees.

End of Year message to Avidity Team from Vas

Happy Holidays from Vas and the Novartis team!

Hi everyone,

As we come to the end of 2025, I want to take a moment to say thank you and wish you a happy holiday season.

What you've built at Avidity-the AOC platform and the late-stage programs in DM1, FSHD and DMD-is remarkable. You've taken on some of the most devastating neuromuscular diseases and brought genuinely new science to the brink of transforming patients' lives. That takes courage, persistence, and a lot of sacrifice from you and your families.

During my visit in November, I saw firsthand your dedication, passion and devotion to patients, and I truly enjoyed spending time with you during our town hall at your offices in San Diego. It was inspiring to see the energy and commitment across the team.

I also recognize that you have many questions about the future as we proceed through our proposed acquisition, and I am genuinely grateful for your patience and professionalism as we work through the process. While some details are still being finalized, here's what we can share with you today:

I know that doesn't remove all the ambiguity, but I hope it gives you a sense of our intent and respect for you and your work.

Thank you again for everything you've done for patients this year. I hope you can disconnect, rest, and spend meaningful time with family and loved ones over the holidays.

Sincerely,

Vas

Additional information and Where to Find It

In connection with the spin-off or sale of Atrium Therapeutics, Inc. ("SpinCo") and the merger by which Novartis AG ("Novartis") will indirectly acquire all outstanding shares of Avidity Biosciences, Inc. ("Avidity") (the "Transactions"), Novartis, Avidity and SpinCo intend to file relevant documents with the Securities and Exchange Commission (the "SEC"), including a definitive proxy statement to be filed by Avidity. The definitive proxy statement and proxy card will be delivered to the stockholders of Avidity in advance of the special meeting relating to the Transactions. This document is not a substitute for the proxy statement or any other document that may be filed by Avidity with the SEC. AVIDITY'S STOCKHOLDERS ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT IN ITS ENTIRETY WHEN IT BECOMES AVAILABLE AND ANY OTHER DOCUMENTS FILED BY EACH OF NOVARTIS AND AVIDITY WITH THE SEC IN CONNECTION WITH THE TRANSACTIONS OR INCORPORATED BY REFERENCE THEREIN BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTIONS AND THE PARTIES TO THE TRANSACTIONS. Investors and security holders will be able to obtain a free copy of the proxy statement and such other documents containing important information about Novartis and Avidity, once such documents are filed with the SEC, through the website maintained by the SEC at www.sec.gov. Novartis and Avidity make available free of charge at the Novartis website at www.novartis.com/investors/financial-data/sec-filings and Avidity's website at investors.aviditybiosciences.com/sec-filings, respectively, copies of documents they file with, or furnish to, the SEC.

Participants in the Solicitation

This communication does not constitute a solicitation of a proxy. Novartis, Avidity and their respective directors, executive officers and certain employees may be deemed to be participants in the solicitation of proxies from the stockholders of Avidity in connection with the Transactions. Information regarding the special interests of these directors and executive officers in the Transactions will be included in the definitive proxy statement referred to above. Security holders may also obtain information regarding the names, affiliations and interests of the Novartis directors and executive officers in the Novartis Annual Report on Form 20-F for the fiscal year ended December 31, 2024, which was filed with the SEC on January 31, 2025. Security holders may obtain information regarding the names, affiliations and interests of Avidity's directors and executive officers in Avidity's definitive proxy statement on Schedule 14A, which was filed with the SEC on April 29, 2025. To the extent the holdings of Avidity's securities by Avidity's directors and executive officers have changed since the amounts set forth in Avidity's definitive proxy statement for its 2025 annual meeting of stockholders, such changes have been or will be reflected on Initial Statements of Beneficial Ownership on Form 3 or Statements of Change in Ownership on Form 4 filed with the SEC. These documents (when available) may be obtained free of charge from the SEC's website at www.sec.gov, the Novartis website at https://www.novartis.com and Avidity's website at investors.aviditybiosciences.com/sec-filings. The contents of the websites referenced above are not deemed to be incorporated by reference into the proxy statement.

No Offer or Solicitation

This communication is for informational purposes only and is not intended to and does not constitute, or form part of, an offer, invitation or the solicitation of an offer or invitation to purchase, otherwise acquire, subscribe for, sell or otherwise dispose of any securities, or the solicitation of any vote or approval in any jurisdiction, pursuant to the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in contravention of applicable law.

Cautionary Statement Regarding Forward-Looking Statements

This communication contains statements that are "forward-looking statements" within the meaning of the United States Private Securities Litigation Reform Act of 1995. Forward-looking statements can generally be identified by words such as "potential," "can," "will," "plan," "may," "could," "would," "expect," "anticipate," "look forward," "believe," "committed," "investigational," "pipeline," "launch," "on track," or similar terms, or by express or implied discussions regarding the proposed acquisition of Avidity and Avidity's related spin-off or sale of SpinCo, the expected timetable for completing each of the proposed Transactions, the composition of the assets and liabilities to be held by SpinCo and Avidity following the spin-off or sale, SpinCo's cash balance, potential marketing approvals, new indications or labeling for Avidity's product candidates, Avidity's platform and preclinical assets, or potential future revenues from Avidity's product candidates. You should not place undue reliance on these statements. Such forward-looking statements are based on our current beliefs and expectations regarding future events, and are subject to significant known and unknown risks and uncertainties. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those set forth in the forward-looking statements. There can be no guarantee that Avidity's investigational products will be submitted or approved for sale or for any additional indications or labeling in any market, or

at any particular time, or that Avidity's approach to the discovery and development of product candidates based on its AOC^™ platform will produce any products of commercial value. There can be no guarantee that the conditions to the closing of the Transactions will be satisfied on the expected timetable or at all or that the expected benefits or synergies from the Transactions will be achieved in the expected timeframe, or at all. In particular, expectations regarding Avidity, SpinCo, or the Transactions could be affected by, among other things, the timing of the satisfaction of customary closing conditions, including the receipt of regulatory approvals and the approval of Avidity's stockholders, on acceptable terms or at all; risks and costs related to the implementation of the separation of SpinCo, including the ability to complete the separation in the anticipated timeframe, or at all, and any changes to the configuration of the businesses included in the separation if implemented; the sale of certain of SpinCo's assets pursuant to a third party right of first negotiation; the risk that competing offers or acquisition proposals will be made; the effects of disruption from the Transactions and the impact of the announcement and pendency of the Transactions on Novartis and/or Avidity's businesses, including their relationships with employees, business partners or governmental entities; the risk that the Transactions may be more expensive to complete than anticipated; the risk that stockholder litigation in connection with the Transactions may result in significant costs of defense, indemnification and liability; a diversion of management's attention from ongoing business operations and opportunities as a result of the Transactions or otherwise; the uncertainties inherent in research and development, including clinical trial results and additional analysis of existing clinical data; regulatory actions or delays or government regulation generally; and the risks and factors referred to in Novartis AG's most recent Annual Report on Form 20-F for the year ended December 31, 2024, Avidity's Annual Report on Form 10-K for the year ended December 31, 2024 and Quarterly Reports on Form 10-Q for the quarters ended March 31, 2025, June 30, 2025 and September 30, 2025, and any subsequent filings made by either party with the SEC, available on the SEC's website at www.sec.gov. Novartis is providing the information in this communication as of this date and does not undertake any obligation to update any forward-looking statements contained in this communication as a result of new information, future events or otherwise, except to the extent required by law.