SUPPLEMENTARY METHODS
STUDY SETTING
The study was performed while schools, daycares, restaurants, bars, and shops were closed. Citizens were allowed to circulate outside their housing in groups of #5 while respecting social distance measures.
LABORATORY PROCEDURES
Plasma was frozen at -80C in the first 24hrs after collection and stored until analysed. All procedures were performed at Laboratory Medicine division and the Geneva Reference Centre for Emerging Viral Diseases.
Reverse-transcription polymerase chain reaction testing criteria. For epidemiological purposes and to maximize
contact tracing, every patient with respiratory symptoms or fever met SARS-CoV-2 reverse- transcription polymerase chain reaction (RT-PCR) testing criteria, independently of epidemiological links. During the study period, there was no restriction in pediatric RT-PCR testing policies when compared to adults. Furthermore, there was no significant shortage of testing capacity in our institution during this time period. Cumulative incidence of RT-PCR confirmed SARS-CoV-2 cases was provided by Geneva’s Office of the Surgeon General.
Rapid diagnostic test (RDT). RDT results were read independently by two collaborators. In case of discordant
reading, a third collaborator also performed the reading to interpret the result. A consensus decision with all three readers was then performed. In the rare case of a faint band, the result was considered negative, as per the
manufacturer’s instructions. Due to the absence of a reference comparison method for IgM testing in our institution (not provided by Euroimmun), we did not assess the rapid IgM detection performances.
STATISTICS
Categorical and continuous variables were compared using the chi-squared and Mann-Whitney tests, respectively, with p-values <0.05 considered significant. The age cut-off of 10 years old for dichotomous comparison of IgG prevalence among study patients was selected prior to the analyses based on previously published studies showing a lower attack rate and/or a lower seroprevalence among children < 10 years old. All statistics were performed using SPSS software, v23.0 (IBM Corp., Armonk, NY).
