Company: DVAX
Filing Date: 2025-05-19
Form Type: DEFA14A
Source: 0001193125-25-122482
Chunk: 0

Company: DYNAVAX TECHNOLOGIES CORP
Filing Date: 2025-05-19
Form: DEFA14A
Chunk 0
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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:

| ☐ | Preliminary Proxy Statement |

| ☐ | Confidential, for Use of the Commission Only (as permitted by Rule 
 14a-6(e)(2))                                                       |

| ☐ | Definitive Proxy Statement |

| ☒ | Definitive Additional Materials |

| ☐ | Soliciting Material Pursuant to §240.14a-12 |

Dynavax Technologies Corporation (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):

| ☒ | No fee required. |

| ☐ | Fee paid previously with preliminary materials. |

| ☐ | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rule 
 14a-6(i)(1) and 0-11.                                                         |

This Schedule 14A filing consists of the following letter distributed by Dynavax Technologies Corporation
(the “Company”) to its stockholders in connection with the Company’s 2025 Annual Meeting of Stockholders. The letter was first used or made available on May 19, 2025.

VOTE TODAY AND PROTECT THE VALUE OF YOUR INVESTMENT IN DYNAVAX!

This is a critical moment for Dynavax – one that requires you to make an important decision that will affect the future value of your investment in the
Company. The Dynavax Board of Directors is singularly focused on enhancing long-term value for all stockholders. We have the right Board, are successfully executing the right strategy and are delivering record financial and operational results. We
have delivered returns of 203% to stockholders over the last five years (as of April 17, 2025, the date Dynavax filed its definitive proxy), far outperforming vaccine peers, which have returned 9%, and the S&P Biotechnology Select
Industry Index, which has declined 17% and Dynavax is one of the few vaccine companies that has returned meaningful capital to stockholders.

Each
of Dynavax’s four director nominees — Brent MacGregor, Scott Myers (our Chairman), Lauren Silvernailand