Seroprevalence of IgG antibodies to SARS-CoV-2 in Geneva, Switzerland (SEROCoV-POP): a population-based study

Stringhini S, Wisniak A, Piumatti G, Azman AS, Lauer SA, Baysson H, De Ridder D, Petrovic D, Schrempft S, Marcus K, Yerly S, Arm Vernez I, Keiser O, Hurst S, Posfay-Barbe KM, Trono D, Pittet D, Gétaz L, Chappuis F, Eckerle I, Vuilleumier N, Meyer B, Flahault A, Kaiser L, Guessous I.
Seroprevalence of anti-SARS-CoV-2 IgG antibodies in Geneva, Switzerland (SEROCoV-POP): a population-based study The Lancet. 2020 Aug 1;396(10247):313-9, doi: 10.1016/S0140-6736(20)31304-0.

Abstract: Assessing the burden of COVID-19 on the basis of the number of medically treated cases is suboptimal, given its dependence on testing strategy, changing case definitions and the wide range of disease presentation. Population-based serological surveys offer a means of estimating infection rates and monitoring the progress of the epidemic, overcoming many of these limitations.

Methods: Using an existing group of adult participants from population-based surveys conducted in Geneva, Switzerland, we conducted a study consisting of 8 weekly serological surveys of these participants and their household members over 5 years of age. We tested each participant for SARS-CoV-2-IgG antibody using a commercially available enzyme-linked immunosorbent assay (Euroimmun AG, Lübeck, Germany). We estimated seroprevalence using a Bayesian regression model, taking into account the performance of the tests and adjusting for the age and sex of the Geneva population.

Results: During the first three weeks, we included 1335 participants from 633 households, with 16% of participants aged under 20 and 53.6% female, a distribution similar to that in Geneva. In the first week, we estimated a seroprevalence of 3.1% (95% Confidence Interval 0.2-5.9, n=343). This increased to 6.1% (95% CI 2.6-9.33, n=416) in week two and to 9.7% (95% CI 6.1-13.11, n=576) in week three. We found that 5-19 year olds (6.0%, 95% CI 2.3-10.2) had a similar seroprevalence to 20-49 year olds (8.5%, 95% CI 4.99-11.7), while significantly lower seroprevalence was observed in those aged 50 and over (3.7%, 95% CI 0.99-6.0, p = 0.0008).

Interpretation: Assuming that the presence of IgG antibodies is at least in the short term associated with immunity, these results highlight that the epidemic is far from dying out simply as a result of herd immunity. What's more, there is no difference in seroprevalence between children and middle-aged adults. These results should be borne in mind at a time when Switzerland and the rest of the world are considering easing restrictions aimed at curbing transmission.

Link to the article in English