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        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001873839</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0001786255</issuerCik>
            <issuerName>ICOSAVAX, INC.</issuerName>
            <secFileNumber>001-40655</secFileNumber>
            <issuerAddress>
                <ns2:street1>1930 Boren Avenue</ns2:street1>
                <ns2:street2>Suite 1000</ns2:street2>
                <ns2:city>Seattle</ns2:city>
                <ns2:stateOrCountry>WA</ns2:stateOrCountry>
                <ns2:zipCode>98101</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>(206) 737-0085</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>ADAM SIMPSON</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
                <relationshipToIssuer>Director</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>40000</noOfUnitsSold>
            <aggregateMarketValue>617056.00</aggregateMarketValue>
            <noOfUnitsOutstanding>50090341</noOfUnitsOutstanding>
            <approxSaleDate>12/21/2023</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>12/21/2023</acquiredDate>
            <natureOfAcquisitionTransaction>Stock Option Exericse</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>40000</amountOfSecuritiesAcquired>
            <paymentDate>12/21/2023</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>ADAM SIMPSON</name>
                <address>
                    <ns2:street1>1930 Boren Avenue</ns2:street1>
                    <ns2:street2>Suite 1000</ns2:street2>
                    <ns2:city>Seattle</ns2:city>
                    <ns2:stateOrCountry>WA</ns2:stateOrCountry>
                    <ns2:zipCode>98101</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>12/20/2023</saleDate>
            <amountOfSecuritiesSold>62205</amountOfSecuritiesSold>
            <grossProceeds>961508.90</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>12/21/2023</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Adam Keith Simpson</signature>
        </noticeSignature>
    </formData>
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144
0001873839
XXXXXXXX
LIVE
0001786255
ICOSAVAX, INC.
001-40655
1930 Boren Avenue
Suite 1000
Seattle
WA
98101
(206) 737-0085
ADAM SIMPSON
Officer
Director
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Floor
New York
NY
10004
40000
617056.00
50090341
12/21/2023
NASDAQ
Common
12/21/2023
Stock Option Exericse
Issuer
N
40000
12/21/2023
Cash
N
ADAM SIMPSON
1930 Boren Avenue
Suite 1000
Seattle
WA
98101
Common
12/20/2023
62205
961508.90
12/21/2023
/s/ Adam Keith Simpson