Company: DVAX
Filing Date: 2025-02-20
Form Type: DEFA14A
Source: 0001193125-25-029819
Chunk: 0

Company: DYNAVAX TECHNOLOGIES CORP
Filing Date: 2025-02-20
Form: DEFA14A
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 19, 2025 Dynavax Technologies Corporation (Exact name of Registrant as Specified in Its Charter)

| Delaware                     |     | 001-34207   |     | 33-0728374         |
| (State or Other Jurisdiction 
 of Incorporation)            |     | -Commission 
 File Number |     | -IRS Employer      
 Identification No. |

| 2100 Powell Street, Suite 720            |     |           |
| Emeryville, California                   |     |     94608 |
| (Address of Principal Executive Offices) |     | -Zip Code |

Registrant’s Telephone Number, Including Area Code: 510 848-5100 (Former Name or Former Address, if Changed Since Last Report) Check the appropriate box below if the Form 8-Kfiling is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

| ☐ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |

| ☒ | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 
 CFR 240.14a-12)                                                        |

| ☐ | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |

| ☐ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |

Securities registered pursuant to Section 12(b) of the Act:

| Title of each class             |     | Trading   
 Symbol(s) |     | Name of each exchange       
 on which registered         |
| Common Stock, $0.001 par value  |     | DVAX      |     | Nasdaq Global Select Market |
| Preferred Share Purchase Rights |     | N/A       |     | Nasdaq Global Select Market |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2of the Securities Exchange Act of 193