United States securities and exchange commission logo

                              June 14, 2021

       Adam Simpson
       Chief Executive Officer
       Icosavax, Inc.
       1616 East Lake Avenue E
       Suite 208
       Seattle, WA 98102

                                                        Re: Icosavax, Inc.
                                                            Draft Registration
Statement on Form S-1
                                                            Filed May 14, 2021
                                                            CIK 0001786255

       Dear Mr. Simpson:

              We have reviewed your draft registration statement and have the
following comments. In
       some of our comments, we may ask you to provide us with information so
we may better
       understand your disclosure.

              Please respond to this letter by providing the requested
information and either submitting
       an amended draft registration statement or publicly filing your
registration statement on
       EDGAR. If you do not believe our comments apply to your facts and
circumstances or do not
       believe an amendment is appropriate, please tell us why in your

             After reviewing the information you provide in response to these
comments and your
       amended draft registration statement or filed registration statement, we
may have additional

       Draft Registration Statement on Form S-1

       Prospectus Summary
       Overview, page 1

   1.                                                   We note your claim that
RSV and hMPV are two of the "leading" causes of pneumonia.
                                                        However, your
disclosure on page 97 indicates that fewer than 20% of adults hospitalized
                                                        with pneumonia had the
RSV or hMPV pathogen and that three pathogens were more
                                                        common. Please explain
to us why it is appropriate to describe RSV and hMPV as
                                                        "leading" causes of
pneumonia in older adults or revise your disclosure.
   2.                                                   You have provided
expected dates for the beginning of clinical trials in instances where it
 Adam Simpson
FirstName  LastNameAdam Simpson
Icosavax, Inc.
June       NameIcosavax, Inc.
     14, 2021
June 14,
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         is unclear whether you have completed clinical trials and/or submitted
INDs. Please
         refrain from making predictions that assume successful preclinical
trails and FDA
         approvals of INDs. Also, remove statements indicating when data is
expected with
         respect to trials that have not yet started.
3.       Please explain the meaning of the term "bivalent" the first time it is
IVX-A12 (RSV-hMPV vaccine candidate), a bivalent combination of IVX-121 (RSV
candidate) and IVX-241 (hMPV vaccine candidate), page 3

4.       We note your disclosure that you intend to submit an IND to the FDA
for IVX-A12, a
         combination of IVX-121 and IVX-241, following completion of your
clinical trial of IVX-
         121 (assuming favorable results). Please revise here and in the
Business section to
         disclose whether you have discussed this development plan with the FDA
and, if so,
         whether you have received any feedback.

         Please also revise to briefly discuss the potential for immunologic
interference between
         your two product candidates that are anticipated to comprise IVX-A12,
as discussed on
         page 15.
Our Programs, page 3

5.       Please revise the disclosure accompanying your pipeline chart to
reflect your disclosure
         elsewhere in your prospectus that your product candidates and
underlying technology are
         licensed from the University of Washington and NIH.
6.       Please explain the current status of IVX-121. The footnote indicates
that its development
         will transition to evaluation as part of IVX-A12, does this mean that
you will not be
         developing IVX-121 as a standalone product candidate? Please also
explain why it is not
         depicted as a solid line, as the other candidates are.
7.       We note you describe IVX-A12 as your "lead product candidate."
However, we note it is
         not the most advanced in terms of development. Please explain what
make it your "lead
SARS-CoV-2, page 3

8.       Please revise your disclosure in this section to disclose whether you
have submitted an
         clinical trial application for IVX-411. Please also revise to reflect
your disclosure on
         pages 20-21 and 108 indicating that SK Bioscience also has a license
to develop product
         candidates based on the same UW VLP technology that you have licensed
and has
         initiated a Phase 1 clinical trial in South Korea for a product
candidate that is similar to
Our Team and Investors, page 4

9.       We note that you identify various entities as investors in your
company here and on page
 Adam Simpson
FirstName  LastNameAdam Simpson
Icosavax, Inc.
June       NameIcosavax, Inc.
     14, 2021
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         91. However, certain of these entities do not appear to be among your
         stockholders as disclosed on page 156. If material, please expand your
disclosure to
         describe the nature of each such entity's investment in you and
explain to us why
         including this information is appropriate. Please also explain in the
response your plans to
         update investors about any changes these entities make with respect to
their investments in
         your company.
Implications of Being an Emerging Growth Company and a Smaller Reporting
Company, page 6

10.      Please supplementally provide us with copies of all written
communications, as defined in
         Rule 405 under the Securities Act, that you, or anyone authorized to
do so on your behalf,
         present to potential investors in reliance on Section 5(d) of the
Securities Act, whether or
         not they retain copies of the communications.
Risk Factors
Intellectual property discovered through government funded programs may be
subject to federal
regulations such as march-in rights..., page 47

11.      Please revise this risk factor to disclose your product candidates
and/or technology that are
         subject to march-in rights.
Management   s Discussion and Analysis of Financial Condition and Results of
Critical Accounting Policies and Significant Judgments and Estimates
Common Stock Valuation, page 86

12.      Once you have an estimated offering price or range, please explain to
us how you
         determined the fair value of the common stock underlying your equity
issuances and the
         reasons for any differences between the recent valuations of your
common stock leading
         up to the IPO and the estimated offering price. This information will
help facilitate our
         review of your accounting for equity issuances including stock
compensation and
         beneficial conversion features. Please discuss with the staff how to
submit your response.
Intellectual Property, page 112

13.      Please revise to disclose the jurisdictions of your foreign patents
and patent applications.
License Agreement with respect to RSV and Other Pathogens, page 115

14.      Your disclosure at the bottom of page 115 states that you must meet a
minimum royalty
         requirement in the "low to mid figures range" following
commercialization. Please revise
         to provide more specificity.
Material Agreements, page 115

15.      Provisions providing the contracting party the right to terminate the
agreement for failure
         to meet milestone events are material to investors. Please expand your
descriptions of the
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Icosavax, Inc.
June 14, 2021
Page 4
         license agreements in this section to disclose the required milestone
events and the dates
         by which you are required to achieve them.

         Please also revise to (i) disclose which of your product candidates
are subject to the
         license agreements described in this section and (ii) quantify amounts
paid to date under
         each license agreement.
       You may contact Julie Sherman at 202-551-3640 or Brian Casio at
202-551-3676 if you
have questions regarding comments on the financial statements and related
matters. Please
contact Alan Campbell at 202-551-4224 or Suzanne Hayes at 202-551-3675 with any

FirstName LastNameAdam Simpson                                 Sincerely,
Comapany NameIcosavax, Inc.
                                                               Division of
Corporation Finance
June 14, 2021 Page 4                                           Office of Life
FirstName LastName