{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,11]],"date-time":"2026-09-11T23:21:51Z","timestamp":1789168911002,"version":"build-2803163510"},"reference-count":44,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T00:00:00Z","timestamp":1760313600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Epidemiol."],"abstract":"<jats:p>In Germany, a consortium of authority-accredited laboratories (ALM) covered approximately 90% of all severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) polymerase chain reaction (PCR) tests during the COVID-19 pandemic (March 2020 until January 2023), and they likewise conducted serological mass tests for IgG antibodies until May 2021. We analyzed the ALM-observed week-resolved time courses of test-positive fractions of PCR and IgG tests, by least-squares fitting a simple function of the former to the course of the latter. Specifically, we show that scaling and shifting the cumulative sum of previous PCR-positive fractions effectively reproduces the time course of the IgG-positive fraction. The value of 0.14 found for the fitted scaling parameter means that only 14% of those who were tested PCR-positively actually became infected with SARS-CoV-2. This parameter fit further implies that a quarter of the German population already carried IgG antibodies from natural infections in their blood at the turn of the year from 2020 to 2021. To check this fit using a second, independent analysis, we took from the literature the Germany-specific ratio of 1:10 for the ratio between one positive PCR test and the corresponding number of persons actually infected with SARS-CoV-2, and therewith estimated the time course of the latter within the German population. The courses of all three fractions, i.e., both the observed and the fit-estimated IgG-positives and the fit-estimated infected, matched each other well in the period from early December 2020 to May 2021. The extrapolated courses of both the fit-estimated fractions, i.e., those of the IgG-positives and the infected, align well to perfectly with the IgG-positive fraction (92%) reported by the Robert Koch Institute at the end of 2021.<\/jats:p>","DOI":"10.3389\/fepid.2025.1592629","type":"journal-article","created":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T05:26:47Z","timestamp":1760333207000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":3,"title":["A calibration of nucleic acid (PCR) by antibody (IgG) tests in Germany: the course of SARS-CoV-2 infections estimated"],"prefix":"10.3389","volume":"5","author":[{"given":"Michael","family":"G\u00fcnther","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert","family":"Rockenfeller","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Harald","family":"Walach","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2025,10,13]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"57","DOI":"10.3390\/antib8040057","article-title":"IgA: structure, function, and developability","volume":"8","author":"de Sousa-Pereira","year":"2019","journal-title":"Antibodies"},{"key":"B2","article-title":"\u201cInfektiologie\u201d","author":"K\u00f6hler","year":""},{"key":"B3","doi-asserted-by":"publisher","first-page":"10208","DOI":"10.26355\/eurrev_202010_23243","article-title":"Seropositivity rate and diagnostic accuracy of serological tests in 2019-nCoV cases: a pooled analysis of individual studies","volume":"24","author":"Guo","year":"2020","journal-title":"Eur Rev Med Pharmacol Sci"},{"key":"B4","doi-asserted-by":"publisher","first-page":"1265","DOI":"10.1093\/infdis\/jiaa463","article-title":"Differences in antibody kinetics and functionality between severe and mild severe acute respiratory syndrome coronavirus 2 infections","volume":"222","author":"Rijkers","year":"2020","journal-title":"J Infect Dis"},{"key":"B5","doi-asserted-by":"publisher","first-page":"e0325923","DOI":"10.1371\/journal.pone.0325923","article-title":"Detectable SARS-CoV-2 specific immune responses in recovered unvaccinated individuals 250 days post wild type infection","volume":"20","author":"Weigl","year":"2025","journal-title":"PLoS One"},{"key":"B6","doi-asserted-by":"publisher","first-page":"e13239","DOI":"10.1111\/irv.13239","article-title":"High seroprevalence of severe acute respiratory syndrome coronavirus 2 among healthcare workers in Yaound\u00e9, Cameroon after the first wave of Covid-19 pandemic and associated factors","volume":"18","author":"Tejiokem","year":"2024","journal-title":"Influenza Other Respir Viruses"},{"key":"B7","doi-asserted-by":"publisher","first-page":"410","DOI":"10.1093\/ije\/dyab010","article-title":"COVID-19 antibody seroprevalence in Santa Clara County, California","volume":"50","author":"Bendavid","year":"2021","journal-title":"Int J Epidemiol"},{"key":"B8","doi-asserted-by":"publisher","first-page":"2000045","DOI":"10.2807\/1560-7917.ES.2020.25.3.2000045","article-title":"Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR","volume":"25","author":"Corman","year":"2020","journal-title":"Eurosurveillance"},{"key":"B9","doi-asserted-by":"publisher","first-page":"221551","DOI":"10.1098\/rsos.221551","article-title":"Reports of deaths are an exaggeration: all-cause and NAA-test-conditional mortality in Germany during the SARS-CoV-2 era","volume":"10","author":"Rockenfeller","year":"2023","journal-title":"R Soc Open Sci"},{"key":"B10","doi-asserted-by":"publisher","first-page":"1871","DOI":"10.3390\/jcm9061871","article-title":"Performance assessment of SARS-CoV-2 PCR assays developed by WHO referral laboratories","volume":"9","author":"Etievant","year":"2020","journal-title":"J Clin Med"},{"key":"B11","first-page":"A2297\/A2031","article-title":"Antigentests auf SARS-CoV-2: was die Aussagekraft bestimmt","volume":"119","author":"Schlenger","year":"2022","journal-title":"Dtsch \u00c4rztebl"},{"key":"B12","doi-asserted-by":"publisher","first-page":"eabd5393","DOI":"10.1126\/sciadv.abd5393","article-title":"Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening","volume":"7","author":"Larremore","year":"2021","journal-title":"Sci Adv"},{"key":"B13","doi-asserted-by":"publisher","first-page":"2001483","DOI":"10.2807\/1560-7917.ES.2020.25.32.2001483","article-title":"Duration of infectiousness and correlation with RT-PCR cycle threshold values in cases of COVID-19, England, January to May 2020","volume":"25","author":"Singanayagam","year":"2020","journal-title":"Eurosurveillance"},{"key":"B14","doi-asserted-by":"publisher","first-page":"237","DOI":"10.1016\/j.jinf.2021.05.022","article-title":"The performance of the SARS-CoV-2 RT-PCR test as a tool for detecting SARS-CoV-2 infection in the population","volume":"83","author":"Stang","year":"2021","journal-title":"J Infect"},{"key":"B15","doi-asserted-by":"publisher","first-page":"470.e1","DOI":"10.1016\/j.cmi.2020.11.009","article-title":"Antibody response using six different serological assays in a completely PCR-tested community after a coronavirus disease 2019 outbreak\u2014the CoNAN study","volume":"27","author":"Weis","year":"2021","journal-title":"Clin Microbiol Infect"},{"key":"B16","doi-asserted-by":"publisher","first-page":"e00904","DOI":"10.1128\/Spectrum.00904-21","article-title":"Risk factors for being seronegative following SARS-CoV-2 infection in a large cohort of health care workers in Denmark","volume":"9","author":"Johannesen","year":"2021","journal-title":"Microbiol Spectr"},{"key":"B17","doi-asserted-by":"publisher","first-page":"CD013652","DOI":"10.1002\/14651858.CD013652.pub2","article-title":"Antibody tests for identification of current and past infection with SARS-CoV-2","volume":"11","author":"Fox","year":"2022","journal-title":"Cochrane Database Syst Rev"},{"key":"B18","doi-asserted-by":"publisher","first-page":"923525","DOI":"10.3389\/fpubh.2022.923525","article-title":"Accuracy of serological tests for COVID-19: a systematic review and meta-analysis","volume":"10","author":"Zheng","year":"2022","journal-title":"Front Public Health"},{"key":"B19","doi-asserted-by":"publisher","first-page":"5829","DOI":"10.1038\/s41467-020-19509-y","article-title":"Infection fatality rate of SARS-CoV2 in a super-spreading event in Germany","volume":"11","author":"Streeck","year":"2020","journal-title":"Nat Commun"},{"key":"B20","doi-asserted-by":"publisher","first-page":"2797","DOI":"10.1007\/s42770-024-01446-3","article-title":"Performance assessment of a new serological diagnostic test for COVID-19 with candidate peptides from spike and nucleocapsid viral proteins","volume":"55","author":"Melo de Cavalcanti-Dantas","year":"2024","journal-title":"Braz J Microbiol"},{"key":"B21","doi-asserted-by":"publisher","first-page":"1772","DOI":"10.1093\/infdis\/jiaa523","article-title":"I. Rodr\u00edguez-Barraquer, are seroprevalence estimates for severe acute respiratory syndrome Coronavirus 2 biased?","volume":"222","author":"Takahashi","year":"2020","journal-title":"J Infect Dis"},{"key":"B22","doi-asserted-by":"publisher","first-page":"529","DOI":"10.1111\/irv.12841","article-title":"Diagnostic performance of COVID-19 serological assays during early infection: a systematic review and meta-analysis of 11 516 samples","volume":"15","author":"Zhang","year":"2021","journal-title":"Influenza Other Respir Viruses"},{"key":"B23","article-title":"Graphical panels showing weekly counts of PCR and IgG tests, Corona-Diagnostik insights provided through ALM Service GmbH, Berlin, Germany","year":""},{"key":"B24","article-title":"ALM-Datenerhebung zur SARS-CoV-2-Testung der Labore (2023)","year":""},{"key":"B25","volume-title":"Two Files: The Weekly Counts of Each PCR and IgG Tests","author":"G\u00fcnther","year":"2024"},{"key":"B26","article-title":"Studie zur Untersuchung des Corona-Infektionsrisikos im \u00f6ffentlichen Personen-Nahverkehr\u2014epidemiologischer Studienbericht (Tech. Rep.)","year":""},{"key":"B27","doi-asserted-by":"publisher","first-page":"313","DOI":"10.4414\/smf.2020.08537","article-title":"Seroprevalence of anti-SARS-CoV-2 IgG antibodies in Geneva, Switzerland (SEROCoV-POP): a population-based study","volume":"396","author":"Stringhini","year":"2020","journal-title":"Lancet"},{"key":"B28","doi-asserted-by":"publisher","first-page":"422","DOI":"10.4414\/fms.2020.08537","article-title":"Seropr\u00e4valenz-Erhebungen als Marker der Immunit\u00e4t der Bev\u00f6lkerung gegen SARS-CoV-2","volume":"20","author":"Wisniak","year":"2020","journal-title":"Swiss Med Forum"},{"key":"B29","doi-asserted-by":"publisher","first-page":"19","DOI":"10.2471\/BLT.20.265892","article-title":"Infection fatality rate of COVID-19 inferred from seroprevalence data","volume":"99","author":"Ioannidis","year":"2021","journal-title":"Bull World Health Organ"},{"key":"B30","doi-asserted-by":"publisher","first-page":"151710","DOI":"10.1016\/j.acthis.2021.151710","article-title":"The history of the antibody as a tool","volume":"123","author":"Packer","year":"2021","journal-title":"Acta Histochem"},{"key":"B31","article-title":"Corona-monitoring bundesweit\u2014Welle 2","author":"G\u00f6\u00dfwald","year":""},{"key":"B32","article-title":"Informationen zur Studie \u201cCorona-Monitoring bundesweit\u201d (CoMoBu-Studie)","author":"G\u00f6\u00dfwald","year":""},{"key":"B33","doi-asserted-by":"publisher","first-page":"1453","DOI":"10.1007\/s15010-023-02011-0","article-title":"Seroprevalence trends of anti-SARS-CoV-2 antibodies and associated risk factors: a population-based study","volume":"51","author":"Tancredi","year":"2023","journal-title":"Infection"},{"key":"B34","doi-asserted-by":"publisher","first-page":"19492","DOI":"10.1038\/s41598-022-23821-6","article-title":"Nationally representative results on SARS-CoV-2 seroprevalence and testing in Germany at the end of 2020","volume":"12","author":"Neuhauser","year":"2022","journal-title":"Sci Rep"},{"key":"B35","article-title":"Corona-Monitoring bundesweit (RKI-SOEP-Studie)\u2014\u00dcberblick zu ersten Ergebnissen","author":"G\u00f6\u00dfwald","year":""},{"key":"B36","doi-asserted-by":"publisher","first-page":"66","DOI":"10.1186\/s13690-023-01072-9","article-title":"Comparing the incidence of SARS-CoV-2 across age groups considering sampling biases\u2014use of testing data of autumn 2021 in Belgium","volume":"81","author":"Lajot","year":"2023","journal-title":"BMC Arch Public Health"},{"key":"B37","doi-asserted-by":"publisher","first-page":"m1808","DOI":"10.1136\/bmj.m1808","article-title":"Interpreting a covid-19 test result","volume":"369","author":"Watson","year":"2020","journal-title":"Br Med J"},{"key":"B38","doi-asserted-by":"publisher","first-page":"359","DOI":"10.1007\/s10441-020-09393-w","article-title":"The epistemology of a positive SARS-CoV-2 test","volume":"69","author":"Klement","year":"2021","journal-title":"Acta Biotheor"},{"key":"B39","doi-asserted-by":"publisher","first-page":"19","DOI":"10.1038\/s43856-022-00080-0","article-title":"Nationwide increases in anti-SARS-CoV-2 IgG antibodies between October 2020 and March 2021 in the unvaccinated Czech population","volume":"2","author":"Piler","year":"2022","journal-title":"Commun Med"},{"key":"B40","doi-asserted-by":"publisher","first-page":"04078","DOI":"10.7189\/jogh.15.04078","article-title":"Evidence of rapid rise in population immunity from SARS-CoV-2 subclinical infections through pre-vaccination serial serosurveys in Pakistan","volume":"15","author":"Iqbal","year":"2025","journal-title":"J Glob Health"},{"key":"B41","doi-asserted-by":"publisher","first-page":"e75","DOI":"10.1017\/S0950268823000584","article-title":"SARS-CoV-2 seroprevalence and determinants for salivary seropositivity among pupils and school staff: a prospective cohort study","volume":"151","author":"Merckx","year":"2023","journal-title":"Epidemiol Infect"},{"key":"B42","doi-asserted-by":"publisher","first-page":"e1004107","DOI":"10.1371\/journal.pmed.1004107","article-title":"Global SARS-CoV-2 seroprevalence from January 2020 to April 2022: a systematic review and meta-analysis of standardized population-based studies","volume":"19","author":"Bergeri","year":"2022","journal-title":"PLoS Med"},{"key":"B43","article-title":"Leserbriefe zu \u201cZahlenchaos Corona\u201d (reader\u2019s letter #17)","author":"Martin","year":""},{"key":"B44","article-title":"Ist die Mehrheit der deutschen Bev\u00f6lkerung bereits gegen Corona immun?","author":"Luckhaus","year":""}],"container-title":["Frontiers in Epidemiology"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fepid.2025.1592629\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,13]],"date-time":"2025-10-13T05:26:49Z","timestamp":1760333209000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fepid.2025.1592629\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,10,13]]},"references-count":44,"alternative-id":["10.3389\/fepid.2025.1592629"],"URL":"https:\/\/doi.org\/10.3389\/fepid.2025.1592629","relation":{},"ISSN":["2674-1199"],"issn-type":[{"value":"2674-1199","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,10,13]]},"article-number":"1592629"}}