{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,16]],"date-time":"2026-04-16T03:57:27Z","timestamp":1776311847255,"version":"3.50.1"},"reference-count":24,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2023,11,9]],"date-time":"2023-11-09T00:00:00Z","timestamp":1699488000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100008868","name":"Science and Technology Department of Jiangsu Province","doi-asserted-by":"publisher","award":["BK20221169"],"award-info":[{"award-number":["BK20221169"]}],"id":[{"id":"10.13039\/501100008868","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Public Health"],"abstract":"<jats:sec><jats:title>Background<\/jats:title><jats:p>China discontinued the zero-COVID-19 policy on December 7, 2022, and then COVID-19 surged mid-December 2022 through mid-January 2023. However, the actual incidence was unknown. This study aimed to estimate the incidence of SARS-CoV-2 infection in children shortly after ending the zero-COVID-19 policy.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>This multicenter cross-sectional study included 1,065 children aged 8\u2009months to 12\u2009years from seven hospitals at six regions across Jiangsu province, based on the convenience sampling, from February 10 to March 10, 2023. Group I comprised 324 children aged 8\u2009months\u20132\u2009years without COVID-19 vaccination, group II consisted of 338 preschool children aged 3\u20135\u2009years with varied vaccination history, and group III contained 403 primary school children aged 6\u201312\u2009years with mostly vaccinated. The COVID-19 vaccines were composed of inactivated SARS-CoV-2. In addition, 96 children\u2019s sera collected in 2014 were included as negative controls. IgG and IgM antibodies against nucleocapsid (N) and subunit 1 of spike (S1) of SARS-CoV-2 (anti-N\/S1) were measured with commercial kits (YHLO Biotech, Shenzhen, China).<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>None of the 96 children (5.1\u2009\u00b1\u20093.5\u2009years; 58.3% boys) in 2014 was positive for anti-N\/S1 IgG or IgM. Of the 1,065 children (5.0\u2009\u00b1\u20093.5\u2009years; 56.0% boys), 988 (92.8%) were anti-N\/S1 IgG positive but none was anti-N\/S1 IgM positive. The positive rate of anti-N\/S1 IgG in Group I, II, and III was 90.4, 88.5, and 98.3%, respectively, with significantly higher in group III than in groups I and II (<jats:italic>p<\/jats:italic>\u2009&amp;lt;\u20090.0001). The median antibody titers in group III (381.61\u2009AU\/ml) were much higher than that in group I (38.34\u2009AU\/ml) and II (51.88\u2009AU\/ml; <jats:italic>p<\/jats:italic>\u2009&amp;lt;\u20090.0001).<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>More than 90% children experienced SARS-CoV-2 infection shortly after ending zero-COVID-19 policy in China, much higher than estimated infections by other studies. The widespread SARS-CoV-2 infection in unvaccinated children should be influential on the policy of COVID-19 vaccination in children in the future.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fpubh.2023.1283158","type":"journal-article","created":{"date-parts":[[2023,11,13]],"date-time":"2023-11-13T06:35:23Z","timestamp":1699857323000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":9,"title":["Incidence of SARS-CoV-2 infection in children shortly after ending zero-COVID-19 policy in China on December 7, 2022: a cross-sectional, multicenter, seroepidemiological study"],"prefix":"10.3389","volume":"11","author":[{"given":"Yi-Hua","family":"Zhou","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chenyu","family":"Xu","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yue","family":"Tao","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Meng","family":"Gu","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Guiping","family":"Zhou","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wei","family":"Zhou","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yue","family":"Jin","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jun","family":"Xie","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Biyun","family":"Xu","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wensan","family":"Zhou","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Junhao","family":"Chen","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Weifeng","family":"Shi","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1965","published-online":{"date-parts":[[2023,11,9]]},"reference":[{"key":"ref1","doi-asserted-by":"publisher","first-page":"670669","DOI":"10.3389\/fpubh.2021.670669","article-title":"Occupational 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