<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001874017</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 AVE., SUITE 1000</ns2:street1>
                <ns2:city>Seattle</ns2:city>
                <ns2:stateOrCountry>WA</ns2:stateOrCountry>
                <ns2:zipCode>98101</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>2067370085</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>CASSIA CEARLEY</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</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 Fl.</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>35000</noOfUnitsSold>
            <aggregateMarketValue>548800.00</aggregateMarketValue>
            <noOfUnitsOutstanding>50090341</noOfUnitsOutstanding>
            <approxSaleDate>12/13/2023</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>02/18/2021</acquiredDate>
            <natureOfAcquisitionTransaction>Previously Exercised Stock Options</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>10143</amountOfSecuritiesAcquired>
            <paymentDate>02/18/2021</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>11/15/2021</acquiredDate>
            <natureOfAcquisitionTransaction>Previously Exercised Stock Options</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>22598</amountOfSecuritiesAcquired>
            <paymentDate>11/15/2021</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>03/18/2022</acquiredDate>
            <natureOfAcquisitionTransaction>Previously Exercised Stock Options</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>2259</amountOfSecuritiesAcquired>
            <paymentDate>03/18/2022</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>12/13/2023</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>02/03/2023</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Cassia Cearley</signature>
        </noticeSignature>
    </formData>
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144
0001874017
XXXXXXXX
LIVE
0001786255
ICOSAVAX INC
001-40655
1930 BOREN AVE., SUITE 1000
Seattle
WA
98101
2067370085
CASSIA CEARLEY
Officer
COMMON
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Fl.
New York
NY
10004
35000
548800.00
50090341
12/13/2023
NASDAQ
Common
02/18/2021
Previously Exercised Stock Options
Issuer
N
10143
02/18/2021
Cash
Common
11/15/2021
Previously Exercised Stock Options
Issuer
N
22598
11/15/2021
Cash
Common
03/18/2022
Previously Exercised Stock Options
Issuer
N
2259
03/18/2022
Cash
Y
12/13/2023
02/03/2023
/s/ Cassia Cearley