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. 2021 Oct 12;116(2):128–136. doi: 10.1080/20477724.2021.1978225

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© 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.

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Figure 1. — Flowchart of the CHRIS COVID-19 study. The study is based on all 13,393 participants to the CHRIS study (2011–18) and their cohabitants. Abbreviations: SAT, serum antibody test; PCR, polymerase chain reaction. Notes: ¹The baseline questionnaire is reported in Additional File 1; ²A random sample of 1450 (augmented to 1812) has been extracted from the 13,393 CHRIS participants to derive population-representative estimates of SARS-CoV-2 infection in the study area (see Methods); ³The follow-up questionnaire is reported in Additional File 2; ⁴Risk of past infection is derived based on responses to the self-administered questionnaires.