The objective of this study is to determine the prevalence and transmission of SARS-CoV-2 infection among Canadian children and parents in the CHILD cohort, identify predictors of infection susceptibility and severity, and understand the health and psychosocial impacts of the COVID-19 pandemic on CHILD families.

Study will leverage the existing CHILD Cohort Study. All household members from each family will be incited to participate. To accommodate institutional physical distancing policies, the study is designed to minimize participant contact and the need for research staff onsite.

Weekly symptom check (by text message): Brief survey will capture COVID-19 signs and symptoms, testing and results, and healthcare utilization. Questions will be aligned with the Government of Canada self-assessment tool and harmonized with international partners.

Quarterly CoRonavIruS Health Impact Survey (CRISIS) (7) and body weight: 10-minute CRISIS survey captures COVID-19 exposure, life changes due to the COVID-19 crisis, daily behaviours, emotions and worries, media use and substance use. Each household member will complete the survey; parents will complete on behalf of younger children. Body weight (measured at home) will also be reported.

Repeated seroprevalence survey: Use of simple home sampling kit containing volumetric absorption micro-sampling devices (Mitra(R) cartridge device, Neoteryx LLC) to collect a fingerstick blood sample (10 ul; a few drops) for SARS-Cov2 IgG serology testing laboratory. Knowledge Users (Public Health authorities) and virology/serology experts will advise on the best available serology assay at the time of testing, and the investigators will consider testing in a public health lab if possible. Kits will be delivered and returned by mail, and an instructional video will be provided. Results will be returned to participants with appropriate explanation of their clinical relevance, and shared in real time with Knowledge Users to inform modeling efforts and pandemic management The timing and frequency of sero-surveys will be guided by our Knowledge Users depending on the progression of the pandemic.

Analysis of recently-collected pre-pandemic bio-samples: To determine the pre-pandemic immune profile of CHILD index children, the investigators will analyze a subset including all cases (asymptomatic and symptomatic) detected by serology and symptom surveys, plus a random subset of uninfected controls (estimated: 400 children in total). The investigators will assess:

1. a panel of innate and adaptive cytokines and chemokines using a commercial multiplex assay,
2. immune cell phenotypes using high dimensional flow cytometry
3. viral antibodies to establish prior/recent infections and cross-reactivity using targeted ELISA assays developed for antibodies to other human beta-coronaviruses

Inclusion Criteria:

• All study participants enrolled in the original CHILD Cohort study are eligible for this add-on study
• Individuals living in the same household as study participants enrolled in the original CHILD Cohort Study are also eligible for this add-on study

Exclusion Criteria:

• CHILD Cohort Study participants who have been previously withdrawn from the study are not eligible for this add-on study
• CHILD Cohort Study participants who have not agreed to future contact by the study team are not eligible for this add-on study
• Participants (with the exception of children) who are not able to provide consent on their own behalf are not eligible for this add-on study
• Participants (with the exception of children) who are not able to read, write and understand English are not eligible for this add-on study
• Participants residing outside of Canada will not be participating in the sample collection component of this study

The study will seek the participation of the original families recruited into the CHILD Cohort Study (child and one or both of their parents or guardians) and any additional interested members from the same household (e.g siblings, grandparents etc). The CHILD Cohort Study is a general population cohort of 3500 families (~12,000 individuals) with children born in BC, Alberta, Manitoba and Ontario. Pregnant mothers were recruited into the study in 2009-2012.

Exclusion criteria for initial recruitment to the CHILD study was mothers pregnant with more than one baby, had in-vitro fertilization (IVF) to become pregnant, baby had severe health problems at birth or was born prior to 35 weeks gestation.

Study data will be entered into REDCap and OpenSpecimen. Questionnaires/forms will only collect de-identified information using the study number. When the questionnaires/ forms collect postal code, the fields will be flagged as containing identifying information. Names and email addresses will be used to send out online questionnaire reminders to participants. All other identifying information will be stored separately from study data, password protected and accessed only by local staff who contact participants. Study participant research data, which is for purposes of statistical analysis and scientific reporting, will be transmitted to and stored at the NCC. This will not include the participant's contact or identifying information. Questionnaire and analyzed data, once cleaned will be de-identified and shared with other approved research team members. At the end of the study, all study databases will be de-identified and archived at the NCC.

Study data will be retained indefinitely.

All IPD will be kept behind two security measures or as per equivalent institutional policy, under the supervision of the site Principal Investigator and will not be transferred outside of the study site. The study monitor, auditor and representatives of the Research Ethics Board (REB) may inspect all documents and records required to be maintained by the Principal Investigator, including but not limited to, medical records for the participants in this study. The study site will permit access to such records. Access to stored samples at the laboratory will be limited to the approved research team. When the study is completed, access to the de-identified, archived study data and/or samples will be provided through the CHILDdb (database).