We warmly thank all the participants and their parents/guardians who agreed to participate in the IRYIS, CHOIR and EnCORE studies. We also thank the nurses and research coordinators from each participating center. We want to recognize the work of the Sainte-Justine University Hospital Mother Child Biobank personnel for processing and storing the samples from the studies. Special thanks to Jocelyne Ayotte, Jessie Beauchemin, Vanessa Truong, Annie Bilodeau, Amal Abdi and Guillaume Bourdel for their role in sample preparation. We also want to acknowledge the work of the EnCORE team in the realization of the study. We are grateful to Mélanie Desjardins, Laura Pierce, Adrien Saucier, Katia Charland, and Carla Benea, who had important roles in the CHOIR and EnCORE studies. Antigens, protein standards, and secondary antibodies for the serum ELISA were kindly provided by The Pandemic Response Challenge Program of the National Research Council of Canada (Dr. Yves Durocher). We would like to thank Tulunay R. Tursun, Martina Tersigni, and the Network Biology Collaborative Centre High-Throughput Screening Facility (RRID: SCR_025390) at the Lunenfeld-Tanenbaum Research Institute for assistance with serum ELISAs. The facility is supported by the Canada Foundation for Innovation (CFI) and the Government of Ontario. The IRYIS study (HD, 2223-HQ-000213) was funded by the COVID-19 Immunity Task Force (CITF) and the Public Health Agency of Canada (PHAC). The CHOIR study was funded by the Canadian Institutes of Health Research (CIHR) (KZ, EG3-179445). The EnCORE study was funded by the Public Health Agency of Canada through the COVID-19 Immunity Task Force (KZ, 2021-HQ-000097). HD and SN are supported by the Fonds de Recherche du Québec – Santé through a Senior Clinical Research Scholar award (HD) and a doctoral research scholarship (SN). CQ is supported through the Canada Research Chair (Tier 1) in Infection Prevention: from hospital to the community (CRC-2019-00055). KZ is supported by the Fonds de Recherche du Québec – Santé through a Junior Researcher Scholar award and the Canada Research Chair (Tier 2) in Global Environmental Change and Infectious Diseases (CRC-2024-00035). MB is supported by the Canada Research Chair and the Sentinel North Research Chair at Université Laval, which is funded by the Canada First Research Excellence Fund. The funders had no role in the study design, data collection or analysis, manuscript preparation or the decision to submit for publication.