Background: Assessing the burden of COVID-19 based on medically-attended case counts is suboptimal given its reliance on testing strategy, changing case definitions and the wide spectrum of disease MESHD presentation. Population-based serosurveys provide one avenue for estimating infection MESHD rates and monitoring the progression of the epidemic, overcoming many of these limitations. Methods: Taking advantage of a pool of adult TRANS participants from population-representative surveys conducted in Geneva, Switzerland, we implemented a study consisting of 8 weekly serosurveys among these participants and their household members older than 5 years. We tested each participant for anti-SARS-CoV-2- IgG antibodies SERO using a commercially available enzyme-linked immunosorbent assay SERO (Euroimmun AG, Lubeck, Germany). We estimated seroprevalence SERO using a Bayesian regression model taking into account test performance SERO and adjusting for the age TRANS and sex of Geneva's population. Results: In the first three weeks, we enrolled 1335 participants coming from 633 households, with 16% <20 years of age TRANS and 53.6% female TRANS, a distribution similar to that of Geneva. In the first week, we estimated a seroprevalence SERO of 3.1% (95% CI 0.2-5.99, n=343). This increased to 6.1% (95% CI 2.6-9.33, n=416) in the second, and to 9.7% (95% CI 6.1-13.11, n=576) in the third week. We found that 5-19 year-olds (6.0%, 95% CI 2.3-10.2%) had similar seroprevalence SERO to 20-49 year olds (8.5%, 95%CI 4.99-11.7), while significantly lower seroprevalence SERO was observed among those 50 and older (3.7%, 95% CI 0.99-6.0, p=0.0008). Interpretation: Assuming that the presence of IgG antibodies SERO is at least in the short-term associated with immunity, these results highlight that the epidemic is far from burning MESHD out simply due to herd immunity. Further, no differences in seroprevalence SERO between children TRANS and middle age TRANS adults TRANS are observed. These results must be considered as Switzerland and the world look towards easing restrictions aimed at curbing transmission TRANS.