SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

PROXY STATEMENT PURSUANT TO SECTION 14(a) OF

THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No.  )

Filed by the Registrant [  ]

Filed by a Party Other than the Registrant [X]

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

[X] Definitive Additional Materials

[  ] Soliciting Material Pursuant to Rule 14a-11(c) or Rule 14a-12

Adverum Biotechnologies, Inc.

(Name of registrant as specified in its charter)

THE SONIC FUND II, L.P.

LAWRENCE KAM

JEAN BENNETT

JODI COOK

HERBERT HUGHES

 (Name of person(s) filing proxy statement, if other than the registrant)

Payment of Filing Fee (Check the Appropriate Box):

[X] No fee required.

[  ] Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

(1) Title of each class of securities to which transaction applies:

(2) Aggregate number of securities to which transaction applies:

(3) Per unit price or other underlying value of transaction computed pursuant to
Exchange Act Rule 0-11 (set forth the amount on which the filing fee is
calculated and state how it is determined):

(4) Proposed maximum aggregate value of transaction:

(5) Total fee paid:

[  ] Fee paid previously with preliminary materials:

[  ] Check box if any part of the fee is offset as provided by Exchange Act
Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the form or schedule and the date of its filing.

(1) Amount Previously Paid:

(2) Form, Schedule or Registration Statement no.:

(3) Filing Party:

(4) Date Filed:

The Sonic Fund II, L.P., together with the other participants named herein (collectively, “Sonic”), has filed with the Securities and Exchange Commission a definitive proxy statement and an accompanying proxy card to be used to solicit votes for the election of its slate of director nominees for the Board of Directors of Adverum Biotechnologies, Inc., a Delaware corporation (the “Issuer”) at the Issuer’s 2021 annual meeting of stockholders.

On May 6, 2021, Sonic and its affiliates made updates to their website (www.saveadverum.com) to post certain press releases made by Sonic and filed with the Securities and Exchange Commission as definitive additional materials on Schedule 14A on May 4, 2021 and the date hereof, respectively. Attached are screenshots of the updated website pages.