Seroconversion of SARS-Cov-2 IgG Antibodies in Chinese Children aged 3-17 years following COVID-19 vaccination

Seroconversion of SARS-Cov-2 IgG Antibodies in Chinese Children aged 3-17 years following COVID-19 vaccination | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Seroconversion of SARS-Cov-2 IgG Antibodies in Chinese Children aged 3-17 years following COVID-19 vaccination Linlin Wang, Suling Wu, Gongbo Zeng, Yuxia Zhu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9332864/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Objectives To investigate the seroconversion rate and dynamics of serum IgG antibodies following Coronavirus Disease 2019(COVID-19) vaccination in children. Methods A total of 3561 children aged 3–17 years who were hospitalized at Hangzhou Children’s Hospital between July 2021 and November 2022, had received COVID-19 vaccination, and had no history of COVID-19 infection were enrolled. SARS-CoV-2 IgG antibodies were detected using the colloidal gold method. Participants were stratified by post-vaccination duration, age group, and sex for analysis of IgG seroconversion rates. Fourfold table data were analyzed using the chi-square (χ²) test, while multi-row and multi-column data were assessed using the χ² partitioning method for pairwise comparisons of multiple sample rates. Results A total of 315 children who received one dose of the vaccine were stratified into groups based on post-vaccination intervals: within half a month, half a month to 1 month, 1–2 months, and > 2 months. Comparative analysis revealed that the IgG seroconversion rates in the half a month–1 month and 1–2 months groups were significantly higher than those in the other two groups (P < 0.0083). Among 3,246 children who received two vaccine doses, stratification by post-vaccination intervals (≤ 1 month, 1–6 months, 6–9 months, and 9–13 months) revealed that the IgG seroconversion rate in the ≤ 1-month group was significantly higher than those in the 1–6-month, 6–9-month, and 9–13-month groups (P < 0.0083). Furthermore, a progressive decline in seroconversion rates was observed with increasing time post-vaccination (P < 0.0083). Comparative analysis by age group demonstrated that the IgG seroconversion rate in children aged 3–6 years was significantly higher than those in the 6–11 and 11–17 years groups (P < 0.0167). Older age groups exhibited significantly lower IgG seroconversion rates (P < 0.0167). Moreover, with prolonged time post-vaccination, the age-dependent decline in seroconversion became more pronounced (P 0.05). However, during the 1–6 month period post-vaccination, girls demonstrated significantly higher IgG seroconversion rates than boys (P 0.05). Conclusion Children who received two doses of the vaccine had a significantly higher rate of IgG antibody seroconversion and a longer duration of maintenance compared to those who received only one dose. The younger the children, the higher the rate of IgG antibody seroconversion and the longer the duration of maintenance. There was no significant difference in the immune response between boys and girls, but the antibody persistence time was longer in girls than in boys. The ability of children to generate an immune response after vaccination was not related to ordinary infection. Trial registration: This research has been registered in the National Medical Research Registration and Filing Information System(registration number : MR-31-24-012692). COVID-19 infection COVID-19 vaccine SARS-CoV-2 IgG antibodies Children Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 13 May, 2026 Reviewers agreed at journal 05 May, 2026 Reviewers invited by journal 28 Apr, 2026 Editor invited by journal 09 Apr, 2026 Editor assigned by journal 08 Apr, 2026 Submission checks completed at journal 08 Apr, 2026 First submitted to journal 06 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9332864","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":635046455,"identity":"0d0af95a-07d4-4cc0-9d84-48dea2ce4b6f","order_by":0,"name":"Linlin Wang","email":"","orcid":"","institution":"Hangzhou Children's Hospital","correspondingAuthor":false,"prefix":"","firstName":"Linlin","middleName":"","lastName":"Wang","suffix":""},{"id":635046456,"identity":"f3e8ac7c-ee73-4473-8a7f-326243d4a55f","order_by":1,"name":"Suling Wu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYLCCBwYMDGzszQcffDCwkSNOSwJQCx/PsWTDGQVpxkRqAWI5iRw1aZ4PhxMJqja4kf5MIqHgjl2bRA6btI0BcwID++GjG/BryTGTSDB4ltzG8/awdY4BWx4DT1raDXxazG7ksAG1HE5mY89LvJ1jwFPMIMFjRkALyGEgLQw5BtIWBhKJDYS1JIAcdtiOjSPHSJrBwICwFvszb4wtgFoS2ECB3GOQYMxGyC+S7ekPb3z4c9hevh0YlT/+/JfjZz98DK8WGEhsgLHYiFEOdiCxCkfBKBgFo2AEAgB/HUoq/aq4HAAAAABJRU5ErkJggg==","orcid":"","institution":"Hangzhou Children's Hospital","correspondingAuthor":true,"prefix":"","firstName":"Suling","middleName":"","lastName":"Wu","suffix":""},{"id":635046457,"identity":"fb35f729-68fd-4545-a225-f5134671cd75","order_by":2,"name":"Gongbo Zeng","email":"","orcid":"","institution":"Hangzhou Children's Hospital","correspondingAuthor":false,"prefix":"","firstName":"Gongbo","middleName":"","lastName":"Zeng","suffix":""},{"id":635046458,"identity":"b4c83d4d-cd18-4286-9366-676afe88facb","order_by":3,"name":"Yuxia Zhu","email":"","orcid":"","institution":"Hangzhou Children's Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yuxia","middleName":"","lastName":"Zhu","suffix":""}],"badges":[],"createdAt":"2026-04-06 10:38:44","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9332864/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9332864/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108806248,"identity":"2a9bb915-bb31-4d30-8254-6c87ab264a65","added_by":"auto","created_at":"2026-05-08 15:28:09","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":461373,"visible":true,"origin":"","legend":"","description":"","filename":"LinlinWang3.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9332864/v1_covered_354aca85-9845-4c69-97e7-7ef51b5a3c03.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Seroconversion of SARS-Cov-2 IgG Antibodies in Chinese Children aged 3-17 years following COVID-19 vaccination","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-pediatrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bped","sideBox":"Learn more about [BMC Pediatrics](http://bmcpediatr.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bped/default.aspx","title":"BMC Pediatrics","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"COVID-19 infection, COVID-19 vaccine, SARS-CoV-2 IgG antibodies, Children","lastPublishedDoi":"10.21203/rs.3.rs-9332864/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9332864/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003eObjectives\u003c/b\u003e\u003c/p\u003e \u003cp\u003eTo investigate the seroconversion rate and dynamics of serum IgG antibodies following Coronavirus Disease 2019(COVID-19) vaccination in children.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eA total of 3561 children aged 3\u0026ndash;17 years who were hospitalized at Hangzhou Children\u0026rsquo;s Hospital between July 2021 and November 2022, had received COVID-19 vaccination, and had no history of COVID-19 infection were enrolled. SARS-CoV-2 IgG antibodies were detected using the colloidal gold method. Participants were stratified by post-vaccination duration, age group, and sex for analysis of IgG seroconversion rates. Fourfold table data were analyzed using the chi-square (χ\u0026sup2;) test, while multi-row and multi-column data were assessed using the χ\u0026sup2; partitioning method for pairwise comparisons of multiple sample rates.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eA total of 315 children who received one dose of the vaccine were stratified into groups based on post-vaccination intervals: within half a month, half a month to 1 month, 1\u0026ndash;2 months, and \u0026gt;\u0026thinsp;2 months. Comparative analysis revealed that the IgG seroconversion rates in the half a month\u0026ndash;1 month and 1\u0026ndash;2 months groups were significantly higher than those in the other two groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0083). Among 3,246 children who received two vaccine doses, stratification by post-vaccination intervals (\u0026le;\u0026thinsp;1 month, 1\u0026ndash;6 months, 6\u0026ndash;9 months, and 9\u0026ndash;13 months) revealed that the IgG seroconversion rate in the \u0026le;\u0026thinsp;1-month group was significantly higher than those in the 1\u0026ndash;6-month, 6\u0026ndash;9-month, and 9\u0026ndash;13-month groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0083). Furthermore, a progressive decline in seroconversion rates was observed with increasing time post-vaccination (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0083). Comparative analysis by age group demonstrated that the IgG seroconversion rate in children aged 3\u0026ndash;6 years was significantly higher than those in the 6\u0026ndash;11 and 11\u0026ndash;17 years groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0167). Older age groups exhibited significantly lower IgG seroconversion rates (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0167). Moreover, with prolonged time post-vaccination, the age-dependent decline in seroconversion became more pronounced (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0167). Comparative analysis by sex revealed no significant difference in IgG seroconversion rates between males and females within 1 month post-vaccination (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05). However, during the 1\u0026ndash;6 month period post-vaccination, girls demonstrated significantly higher IgG seroconversion rates than boys (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). No statistically significant difference was observed in seroconversion rates between infected and non-infected pediatric cases (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusion\u003c/b\u003e\u003c/p\u003e \u003cp\u003eChildren who received two doses of the vaccine had a significantly higher rate of IgG antibody seroconversion and a longer duration of maintenance compared to those who received only one dose. The younger the children, the higher the rate of IgG antibody seroconversion and the longer the duration of maintenance. There was no significant difference in the immune response between boys and girls, but the antibody persistence time was longer in girls than in boys. The ability of children to generate an immune response after vaccination was not related to ordinary infection.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTrial registration:\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis research has been registered in the National Medical Research Registration and Filing Information System(registration number : MR-31-24-012692).\u003c/p\u003e","manuscriptTitle":"Seroconversion of SARS-Cov-2 IgG Antibodies in Chinese Children aged 3-17 years following COVID-19 vaccination","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-07 09:42:01","doi":"10.21203/rs.3.rs-9332864/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-13T16:56:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"295335653819097107279312281772580837589","date":"2026-05-05T12:11:21+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-28T15:56:52+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-09T13:01:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-08T10:06:04+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-08T10:05:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Pediatrics","date":"2026-04-06T10:33:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-pediatrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bped","sideBox":"Learn more about [BMC Pediatrics](http://bmcpediatr.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bped/default.aspx","title":"BMC Pediatrics","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"aa4f010b-5567-42e3-8c0a-e65f4cc7e5d7","owner":[],"postedDate":"May 7th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-13T16:56:36+00:00","index":60,"fulltext":""},{"type":"reviewerAgreed","content":"295335653819097107279312281772580837589","date":"2026-05-05T12:11:21+00:00","index":55,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T09:42:02+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-07 09:42:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9332864","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9332864","identity":"rs-9332864","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}