This Amendment No. 3 (this “Amendment”) to Schedule
14D-9 amends and supplements the Solicitation/Recommendation Statement on Schedule 14D-9 originally filed by Decibel Therapeutics, Inc., a Delaware corporation
(“Decibel”), with the U.S. Securities and Exchange Commission (the “SEC”) on August 25, 2023 (as amended or supplemented from time to time, the “Schedule 14D-9”), with
respect to the tender offer by Symphony Acquisition Sub, Inc., a Delaware corporation (“Purchaser”), and a wholly owned subsidiary of Regeneron Pharmaceuticals, Inc., a New York corporation (“Regeneron”), to acquire all of the
issued and outstanding shares of common stock (the “Shares”), of Decibel in exchange for (i) $4.00 per share, payable in cash, without interest and subject to reduction for any applicable withholding of taxes (the “Cash
Consideration”), plus (ii) one contractual, non-tradeable contingent value right per share (each, a “CVR”), which entitles the holder to potentially receive contingent payments of up to an
aggregate of $3.50 per CVR, without interest and subject to reduction for any applicable withholding taxes, upon the achievement of certain clinical development and regulatory milestones for Decibel’s lead investigational product candidate, DB-OTO, within specified time periods and in accordance with the terms and subject to the conditions of a contingent value rights agreement to be entered into with a rights agent mutually agreeable to Regeneron and
Decibel (the Cash Consideration plus one CVR, together, the “Offer Consideration”), upon the terms and subject to the conditions set forth in the Offer to Purchase, dated as of August 25, 2023 (together with any amendments or
supplements thereto, the “Offer to Purchase”), and in the related Letter of Transmittal (together with any amendments or supplements thereto, the “Letter of Transmittal,” which, together with the Offer to Purchase, constitute the
“Offer”). The Offer is described in a Tender Offer Statement on Schedule TO (as amended or supplemented from time to time, the “Schedule TO”) filed jointly by Regeneron and Purchaser with the SEC on August 25, 2023. The
Offer to Purchase and the Letter of Transmittal have been filed as Exhibits (a)(1)(A) and (a)(1)(B) to the Schedule 14D-9, respectively.
Capitalized terms used in this Amendment but not defined herein shall have the respective meanings given to such terms in the Schedule 14D-9. The information set forth in the Schedule 14D-9 remains unchanged and is incorporated herein by reference, except that such information is hereby amended or
supplemented to the extent specifically provided herein.
Item 8. Additional Information.
Item 8 of the Schedule 14D-9, as amended, is hereby amended and supplemented by adding the following new subsection
before the final subsection entitled “—(g) Forward Looking Statements” (which shall be redesignated as subsection “—(h) Forward-Looking Statements”) at the end of such Item 8:
“(g) Final Results of the Offer and Completion of the Merger
The Offer expired at one minute after 11:59 p.m. Eastern Time, on September 22, 2023 (such date and time, the “Expiration Time”). Computershare,
in its capacity as depositary for the Offer, advised that, as of the Expiration Time, a total of 19,797,530 Shares were validly tendered and not validly withdrawn pursuant to the Offer, which Shares, together with all other Shares beneficially owned
by Purchaser and its affiliates, represent approximately 86.12% of the Shares outstanding as of the Expiration Time. As of the Expiration Time, the number of Shares validly tendered and not validly withdrawn pursuant to the Offer, together with all
other Shares beneficially owned by Purchaser and its affiliates, satisfied the Minimum Condition. After the expiration of the Offer, Purchaser irrevocably accepted for payment all Shares validly tendered and not validly withdrawn pursuant to the
Offer. Purchaser will promptly pay for all such Shares.
As the final step of the acquisition process, Regeneron completed its acquisition of Decibel by
consummating the Merger on September 25, 2023, in accordance with Section 251(h) of the DGCL without a vote of Decibel’s stockholders. At the Effective Time of the Merger, Purchaser was merged with and into Decibel, the separate
existence of Purchaser ceased, and Decibel continued as the Surviving Corporation and a wholly owned subsidiary of Regeneron. Each issued and outstanding Share (other than (i) Shares that were owned by Decibel or held in the treasury of
Decibel, (ii) Shares then held by Regeneron or Purchaser, (iii) Shares then held by any wholly owned subsidiary of Regeneron (other than Purchaser) or any wholly owned subsidiary of Decibel and (iv) Shares with respect to which the
holders thereof have properly exercised and perfected demands for appraisal of such shares in accordance with Section 262 the DGCL) was converted automatically into and thereafter represent only the right to receive the Offer Consideration.