{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,27]],"date-time":"2026-02-27T16:55:55Z","timestamp":1772211355935,"version":"3.50.1"},"reference-count":8,"publisher":"Public Library of Science (PLoS)","issue":"2","license":[{"start":{"date-parts":[[2022,2,3]],"date-time":"2022-02-03T00:00:00Z","timestamp":1643846400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100005632","name":"Narodowe Centrum Bada\u0144 i Rozwoju","doi-asserted-by":"publisher","award":["SZPITALE-JEDNOIMIENNE\/48\/2020"],"award-info":[{"award-number":["SZPITALE-JEDNOIMIENNE\/48\/2020"]}],"id":[{"id":"10.13039\/501100005632","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS ONE"],"abstract":"<jats:p>Population immunity (herd immunity) to SARS-CoV-2 derives from two sources: vaccinations or cases of infection with the virus. Infections can be diagnosed as COVID-19 and registered, or they can be asymptomatic, oligosymptomatic, or even full-blown but undiagnosed and unregistered when patients recovered at home. Estimation of population immunity to SARS-CoV-2 is difficult and remains a subject of speculations. Here we present a population screening for SARS-CoV-2 specific IgG and IgA antibodies in Polish citizens (N = 501) who had never been positively diagnosed with or vaccinated against SARS-CoV-2. Serum samples were collected in Wroc\u0142aw (Lower Silesia) on 15th and 22nd May 2021. Sera from hospitalized COVID-19 patients (N = 22) or from vaccinated citizens (N = 14) served as positive controls. Sera were tested with Microblot-Array COVID-19 IgG and IgA (quantitative) that contain specific SARS-CoV-2 antigens: NCP, RBD, Spike S2, E, ACE2, PLPro protein, and antigens for exclusion cross-reactivity with other coronaviruses: MERS-CoV, SARS-CoV, HCoV 229E Np, HCoV NL63 Np. Within the investigated population of healthy individuals who had never been positively diagnosed with or vaccinated against SARS-CoV-2, we found that 35.5% (178 out of 501) were positive for SARS-CoV-2-specific IgG and 52.3% (262 out of 501) were positive for SARS-CoV-2-specific IgA; 21.2% of the investigated population developed virus-specific IgG or IgA while being asymptomatic. Anti-RBD IgG, which represents virus-neutralizing potential, was found in 25.6% of individuals (128 out of 501). These patients, though positive for anti-SARS-CoV-2 antibodies, cannot be identified in the public health system as convalescents due to undiagnosed infections, and they are considered unaffected by SARS-CoV-2. Their contribution to population immunity against COVID-19 should however be considered in predictions and modeling of the COVID-19 pandemic. Of note, the majority of the investigated population still lacked anti-RBD IgG protection (74.4%); thus vaccination against COVID-19 is still of the most importance for controlling the pandemic.<\/jats:p>","DOI":"10.1371\/journal.pone.0253638","type":"journal-article","created":{"date-parts":[[2022,2,3]],"date-time":"2022-02-03T13:43:28Z","timestamp":1643895808000},"page":"e0253638","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":6,"title":["Hidden fraction of Polish population immune to SARS-CoV-2 in May 2021"],"prefix":"10.1371","volume":"17","author":[{"given":"Wiktoria","family":"Budziar","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Katarzyna","family":"Gembara","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Marek","family":"Harhala","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Aleksander","family":"Szymczak","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6515-5762","authenticated-orcid":true,"given":"Natalia","family":"J\u0119druchniewicz","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Krzysztof","family":"Baniecki","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Aleksandra","family":"Pikies","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Artur","family":"Nahorecki","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Agnieszka","family":"Hoffmann","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1110-6305","authenticated-orcid":true,"given":"Amelia","family":"Karda\u015b","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7629-4912","authenticated-orcid":true,"given":"Alina","family":"Szewczyk-D\u0105browska","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tomasz","family":"Klimek","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7220-3518","authenticated-orcid":true,"given":"Zuzanna","family":"Ka\u017amierczak","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wojciech","family":"Witkiewicz","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kamil","family":"Barczyk","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1518-3183","authenticated-orcid":true,"given":"Krystyna","family":"D\u0105browska","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"340","published-online":{"date-parts":[[2022,2,3]]},"reference":[{"issue":"7840","key":"pone.0253638.ref001","doi-asserted-by":"crossref","first-page":"125","DOI":"10.1038\/s41586-020-2739-1","article-title":"The coding capacity of SARS-CoV-2,\u201d","volume":"589","author":"Y. Finkel","year":"2021","journal-title":"Nature"},{"key":"pone.0253638.ref002","unstructured":"\u201eWHO,\u201d 2020. [Online]. Available: https:\/\/www.who.int\/emergencies\/diseases\/novel-coronavirus-2019\/events-as-they-happen. [Data uzyskania dost\u0119pu: 04 06 2021]."},{"issue":"1","key":"pone.0253638.ref003","doi-asserted-by":"crossref","first-page":"104","DOI":"10.1186\/s12929-020-00695-2","article-title":", \u201eCoronavirus vaccine development: from SARS and MERS to COVID-19,\u201d","volume":"27","author":"Y. D. Li","year":"2020","journal-title":"J Biomed Sci"},{"key":"pone.0253638.ref004","first-page":"711","article-title":"COVID-19 vaccines: rapid development, implications, challenges and future prospects","volume":"34","author":"S. Kashte","year":"2021"},{"issue":"6","key":"pone.0253638.ref005","doi-asserted-by":"crossref","first-page":"e163","DOI":"10.1016\/S1473-3099(20)30837-9","article-title":"\u201eTowards an accurate and systematic characterisation of persistently asymptomatic infection with SARS-CoV-2,\u201d","volume":"21","author":"E. A. Meyerowitz","year":"2021","journal-title":"Lancet Infect Dis."},{"key":"pone.0253638.ref006","doi-asserted-by":"crossref","first-page":"100392","DOI":"10.1016\/j.epidem.2020.100392","article-title":"The time scale of asymptomatic transmission affects estimates of epidemic potential in the COVID-19 outbreak","volume":"31","author":"S. W. Park","year":"2020","journal-title":"Epidemics"},{"key":"pone.0253638.ref007","unstructured":"ICU University of Warsaw, \u201eICM EPIDEMIOLOGICAL MODEL,\u201d 2021. [Online]. Available: https:\/\/covid-19.icm.edu.pl\/en\/current-forecasts\/. [Data uzyskania dost\u0119pu: 02 06 2021]."},{"issue":"10","key":"pone.0253638.ref008","doi-asserted-by":"crossref","first-page":"583","DOI":"10.1038\/s41577-020-00451-5","article-title":"Cauchemez, \u201eCOVID-19 herd immunity: where are we?,\u201d","volume":"20","author":"A. Fontanet i S","year":"2020","journal-title":"Nat Rev Immunol."}],"container-title":["PLOS ONE"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/dx.plos.org\/10.1371\/journal.pone.0253638","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2022,2,3]],"date-time":"2022-02-03T13:43:37Z","timestamp":1643895817000},"score":1,"resource":{"primary":{"URL":"https:\/\/dx.plos.org\/10.1371\/journal.pone.0253638"}},"subtitle":[],"editor":[{"given":"Yury E.","family":"Khudyakov","sequence":"first","affiliation":[],"role":[{"role":"editor","vocabulary":"crossref"}]}],"short-title":[],"issued":{"date-parts":[[2022,2,3]]},"references-count":8,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2022,2,3]]}},"URL":"https:\/\/doi.org\/10.1371\/journal.pone.0253638","relation":{"has-preprint":[{"id-type":"doi","id":"10.1101\/2021.06.22.21258711","asserted-by":"object"}]},"ISSN":["1932-6203"],"issn-type":[{"value":"1932-6203","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,2,3]]}}}