The representative COVID-19 cohort Munich (KoCo19): from the beginning of the pandemic to the Delta virus variant
Authors: Le Gleut Ronan , Plank Michael , Pütz Peter , Radon Katja , Bakuli Abhishek , Rubio-Acero Raquel , Paunovic Ivana , Rieß Friedrich , Winter Simon , Reinkemeyer Christina , Schälte Yannik , Olbrich Laura , Hannes Marlene , Kroidl Inge , Noreña Ivan , Janke Christian , Wieser Andreas , Hoelscher Michael , Fuchs Christiane , Castelletti Noemi ,   the KoCo19/ORCHESTRA-study group, Ahmed Mohamed Ibraheem Mohamed , Alamoudi Emad , Anderson Jared , Baldassarre Valeria , Baumann Maximilian , Becker Marc , Bednarski Franziska , Behlen Marieke , Bemirayev Olimbek , Beyerl Jessica , Bitzer Patrick , Böhnlein Rebecca , Brand Isabel , Brauer Anna , Britz Vera , Bruger Jan , Bünz Franziska , Caroli Friedrich , Coleman Josephine , Contento Lorenzo , Czwienzek Alina , Deák Flora , Diefenbach Maximilian N. , Diepers Paulina , Do Anna , Dobler Gerhard , Durner Jürgen , Eser Tabea , Eberle Ute , Eckstein Judith , Falk Philine , Feyereisen Manuela , Fingerle Volker , Fischer Stefanie , Frese Jonathan , Forster Felix , Fröschl Günter , Geisenberger Otto , Garí Mercè , Gasser Marius , Gauder Sonja , Geier Raffaela , Gillig Kristina , Geldmacher Christof , Gezgin Keisha , Gilberg Leonard , Gillig Kristina , Girl Philipp , Golschan Elias , Grauvogl Vitus , Noller Jessica Michelle Guggenbuehl , Guglielmini Elena Maria , Gutierrez Pablo , Haderer Anselm , Halfmann Celina , Hartinger Lena , Haselwarter Timm , Hasenauer Jan , Hernandez Alejandra , Heller Luca , Heiber Arlett , Herrmann Matthias , Hillari Leah , Hillmann Stefan , Hinske Christian , Hoefflin Janna , Hofberger Tim , Höfinger Michael , Hofmann Larissa , Horn Sacha , Huber Kristina , Janke Christian , Karger Lilian , Kappl Ursula , Keßler Antonia , Khan Zohaib , Kiani Charlotte , Klugherz Isabel , Kreider Norah , Kresin Johanna , Kroidl Arne , Kunder Pratik , Lang Magdalena , Lang Clemens , Lange Silvan , Lapteva Ekaterina , Laxy Michael , Leidl Reiner , Liedl Leopold , Lindner Felix , Lucaj Xhovana , Lucke Elisabeth , Luppa Fabian , Nafziger Alexandra Sophie , Maczka Alexander , Mang Petra , Markgraf Alisa , Matcau Paula , Mayrhofer Rebecca , Mekota Anna-Maria , Metaxa Dafni , Mohr Emily , Müller Hannah , Müller Katharina , Nascimento Nathalia , Niermeyer Kasimir , Nikolaides Sophia , Pattard Leonie , Pleimelding Claire , Pletschette Michel , Poll Viona , Prückner Stephan , Puchinger Kerstin , Pusl Konstantin , Raimúndez Elba , Raschka Julius , Reich Jakob , Reinkemeyer Christina , Rothe Camilla , Ruci Viktoria , Saathoff Elmar , Schäfer Nicole , Schandelmaier Paul , Schluse Benedikt , Schneider Annika , Schneider Lara , Schultz Sophie , Schunk Mirjam , Schwettmann Lars , Sedlmeier Josefin , Sintu-Sempta Linda , Soler Alba , Sothmann Peter , Strobl Katharina , Strüber Aida , Strüber Laura , Tang Jeni , Theis Fabian , Thiel Verena , Thumser Eva , Thur Niklas , Ullrich Julian , Vollmayr Vincent , Von Lovenberg Emilia , Von Lovenberg Jonathan , Vos Carsten , Waibel Julia , Wallrauch Claudia , Weigl Nikolas , Wölfl Roman , Wolff Julia , Wullinger Pia , Würfel Tobias , Wustrow Patrick , Zange Sabine , Zeggini Eleftheria , Zielke Anna , Zimmer Thorbjörn , Zimmermann Thomas , Zielke Anna , Zuche Lea 
Published: July 2023

Abstract
Background
Population-based serological studies allow to estimate prevalence of SARS-CoV-2 infections despite a substantial number of mild or asymptomatic disease courses. This became even more relevant for decision making after vaccination started. The KoCo19 cohort tracks the pandemic progress in the Munich general population for over two years, setting it apart in Europe.

Methods
Recruitment occurred during the initial pandemic wave, including 5313 participants above 13 years from private households in Munich. Four follow-ups were held at crucial times of the pandemic, with response rates of at least 70%. Participants filled questionnaires on socio-demographics and potential risk factors of infection. From Follow-up 2, information on SARS-CoV-2 vaccination was added. SARS-CoV-2 antibody status was measured using the Roche Elecsys® Anti-SARS-CoV-2 anti-N assay (indicating previous infection) and the Roche Elecsys® Anti-SARS-CoV-2 anti-S assay (indicating previous infection and/or vaccination). This allowed us to distinguish between sources of acquired antibodies.

Results
The SARS-CoV-2 estimated cumulative sero-prevalence increased from 1.6% (1.1-2.1%) in May 2020 to 14.5% (12.7-16.2%) in November 2021. Underreporting with respect to official numbers fluctuated with testing policies and capacities, becoming a factor of more than two during the second half of 2021. Simultaneously, the vaccination campaign against the SARS-CoV-2 virus increased the percentage of the Munich population having antibodies, with 86.8% (85.5-87.9%) having developed anti-S and/or anti-N in November 2021. Incidence rates for infections after (BTI) and without previous vaccination (INS) differed (ratio INS/BTI of 2.1, 0.7-3.6). However, the prevalence of infections was higher in the non-vaccinated population than in the vaccinated one. Considering the whole follow-up time, being born outside Germany, working in a high-risk job and living area per inhabitant were identified as risk factors for infection, while other socio-demographic and health-related variables were not. Although we obtained significant within-household clustering of SARS-CoV-2 cases, no further geospatial clustering was found.

Conclusions
Vaccination increased the coverage of the Munich population presenting SARS-CoV-2 antibodies, but breakthrough infections contribute to community spread. As underreporting stays relevant over time, infections can go undetected, so non-pharmaceutical measures are crucial, particularly for highly contagious strains like Omicron.