From first to second wave: follow-up of the prospective COVID-19 cohort (KoCo19) in Munich (Germany)
Authors: Radon Katja , Bakuli Abhishek , Pütz Peter , Le Gleut Ronan , Guggenbuehl Noller Jessica Michelle , Olbrich Laura , Saathoff Elmar , Garí Mercè , Schälte Yannik , Frahnow Turid , Wölfel Roman , Pritsch Michael , Rothe Camilla , Pletschette Michel , Rubio-Acero Raquel , Beyerl Jessica , Metaxa Dafni , Forster Felix , Thiel Verena , Castelletti Noemi , Rieß Friedrich , Diefenbach Maximilian N. , Fröschl Günter , Bruger Jan , Winter Simon , Frese Jonathan , Puchinger Kerstin , Brand Isabel , Kroidl Inge , Wieser Andreas , Hoelscher Michael , Hasenauer Jan , Fuchs Christiane ,   the KoCo19 study group, Ackermann Nikolaus , Alamoudi Emad , Anderson Jared , Baumann Maxilmilian , Becker Marc , Bednarzki Franziska , Bemirayev Olimbek , Bitzer Patrick , Böhnlein Rebecca , Caroli Friedrich , Coleman Josephine , Contento Lorenzo , Czwienzek Alina , Deák Flora , Diekmannshemke Jana , Dobler Gerhard , Durner Jürgen , Eberle Ute , Eckstein Judith , Eser Tabea , Falk Philine , Feyereisen Manuela , Fingerle Volker , Geisenberger Otto , Geldmacher Christof , Gilberg Leonard , Gillig Kristina , Girl Philipp , Golschan Elias , Guglielmini Elena Maria , Gutierrez Pablo , Haderer Anslem , Hannes Marlene , Hartinger Lena , Hernandez Alejandra , Hillari Leah , Hinske Christian , Hofberger Tim , Horn Sacha , Huber Kristina , Janke Christian , Kappl Ursula , Keßler Antonia , Khan Zohaib , Kresin Johanna , Kroidl Arne , Lang Magdalena , Lang Clemens , Lange Silvan , Laxy Michael , Leidl Reiner , Liedl Leopold , Lucaj Xhovana , Luppa Fabian , Nafziger Alexandra Sophie , Mang Petra , Markgraf Alisa , Mayrhofer Rebecca , Müller Hannah , Müller Katharina , Paunovic Ivana , Plank Michael , Pleimelding Claire , Prückner Stephan , Raimúndez Elba , Reich Jakob , Ruci Viktoria , Schäfer Nicole , Schluse Benedikt , Schneider Lara , Schunk Mirjam , Schwettmann Lars , Sing Andreas , Soler Alba , Sothmann Peter , Strobl Kathrin , Tang Jeni , Theis Fabian , Thiesbrummel Sophie , Vollmayr Vincent , von Lovenberg Emilia , von Lovenberg Jonathan , Waibel Julia , Wallrauch Claudia , Wolff Julia , Würfel Tobias , Yaqine Houda , Zange Sabine , Zeggini Eleftheria , Zielke Anna , Zimmer Thorbjörn 
Published: September 2021

Background

In the 2nd year of the COVID-19 pandemic, knowledge about the dynamics of the infection in the general population is still limited. Such information is essential for health planners, as many of those infected show no or only mild symptoms and thus, escape the surveillance system. We therefore aimed to describe the course of the pandemic in the Munich general population living in private households from April 2020 to January 2021.

Methods

The KoCo19 baseline study took place from April to June 2020 including 5313 participants (age 14 years and above). From November 2020 to January 2021, we could again measure SARS-CoV-2 antibody status in 4433 of the baseline participants (response 83%). Participants were offered a self-sampling kit to take a capillary blood sample (dry blood spot; DBS). Blood was analysed using the Elecsys®Anti-SARS-CoV-2 assay (Roche). Questionnaire information on socio-demographics and potential risk factors assessed at baseline was available for all participants. In addition, follow-up information on health-risk taking behaviour and number of personal contacts outside the household (N = 2768) as well as leisure time activities (N = 1263) were collected in summer 2020.

Results

Weighted and adjusted (for specificity and sensitivity) SARS-CoV-2 sero-prevalence at follow-up was 3.6% (95% CI 2.9–4.3%) as compared to 1.8% (95% CI 1.3–3.4%) at baseline. 91% of those tested positive at baseline were also antibody-positive at follow-up. While sero-prevalence increased from early November 2020 to January 2021, no indication of geospatial clustering across the city of Munich was found, although cases clustered within households. Taking baseline result and time to follow-up into account, men and participants in the age group 20–34 years were at the highest risk of sero-positivity. In the sensitivity analyses, differences in health-risk taking behaviour, number of personal contacts and leisure time activities partly explained these differences.

Conclusion

The number of citizens in Munich with SARS-CoV-2 antibodies was still below 5% during the 2nd wave of the pandemic. Antibodies remained present in the majority of SARS-CoV-2 sero-positive baseline participants. Besides age and sex, potentially confounded by differences in behaviour, no major risk factors could be identified. Non-pharmaceutical public health measures are thus still important.