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Are there differences in the odds of household transmission of SARS-CoV-2 by younger children compared with older children?
In this cohort study of 6280 households with pediatric index cases, the adjusted odds of household transmission by children aged 0 to 3 years was 1.43 compared with children aged 14 to 17 years.
Younger children may have greater risk of transmitting SARS-CoV-2 to caregivers and siblings in the household than older children.
As a result of low numbers of pediatric cases early in the COVID-19 pandemic, pediatric household transmission of SARS-CoV-2 remains an understudied topic.
To determine whether there are differences in the odds of household transmission by younger children compared with older children.
Design, Setting, and Participants
This population-based cohort study took place between June 1 and December 31, 2020, in Ontario, Canada. Private households in which the index case individual of laboratory-confirmed SARS-CoV-2 infection was younger than 18 years were included. Individuals were excluded if they resided in apartments missing suite information, in households with multiple index cases, or in households where the age of the index case individual was missing.
Age group of pediatric index cases categorized as 0 to 3, 4 to 8, 9 to 13, and 14 to 17 years.
Main Outcomes and Measures
Household transmission, defined as households where at least 1 secondary case occurred 1 to 14 days after the pediatric index case.
A total of 6280 households had pediatric index cases, and 1717 households (27.3%) experienced secondary transmission. The mean (SD) age of pediatric index case individuals was 10.7 (5.1) years and 2863 (45.6%) were female individuals. Children aged 0 to 3 years had the highest odds of transmitting SARS-CoV-2 to household contacts compared with children aged 14 to 17 years (odds ratio, 1.43; 95% CI, 1.17-1.75). This association was similarly observed in sensitivity analyses defining secondary cases as 2 to 14 days or 4 to 14 days after the index case and stratified analyses by presence of symptoms, association with a school/childcare outbreak, or school/childcare reopening. Children aged 4 to 8 years and 9 to 13 years also had increased odds of transmission (aged 4-8 years: odds ratio, 1.40; 95% CI, 1.18-1.67; aged 9-13 years: odds ratio, 1.13; 95% CI, 0.97-1.32).
Conclusions and Relevance
This study suggests that younger children may be more likely to transmit SARS-CoV-2 infection compared with older children, and the highest odds of transmission was observed for children aged 0 to 3 years. Differential infectivity of pediatric age groups has implications for infection prevention within households, as well as schools/childcare, to minimize risk of household secondary transmission. Additional population-based studies are required to establish the risk of transmission by younger pediatric index cases.
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Corresponding Author: Sarah A. Buchan, PhD, Public Health Ontario, 661 University Ave, Floor 17, Toronto, ON M5G 1M1, Canada (email@example.com).
Accepted for Publication: May 19, 2021.
Published Online: August 16, 2021. doi:10.1001/jamapediatrics.2021.2770
Correction: This article was corrected on September 20 2021, to fix a typo in Table 2.
Author Contributions: Ms Paul and Dr Buchan had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Paul, Daneman, Schwartz, Science, Brown, Buchan.
Acquisition, analysis, or interpretation of data: Paul, Schwartz, Science, Brown, Whelan, Chan, Buchan.
Drafting of the manuscript: Paul.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Paul, Schwartz, Brown.
Administrative, technical, or material support: Paul, Schwartz, Buchan.
Supervision: Science, Buchan.
Conflict of Interest Disclosures: Dr Buchan reported grants from Canadian Institutes of Health Research for research on influenza, respiratory syncytial virus, and COVID-19 and grants from Canadian Immunity Task Force for COVID-19 vaccines outside the submitted work. No other disclosures were reported.
Funding/Support: This study did not have a direct funding source but was supported by Public Health Ontario.
Role of the Funder/Sponsor: The sponsor had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Additional Contributions: We thank James Johnson, MPH, and Arezou Saedi, MD, for conducting the address-matching work; Trevor van Ingen, MPH, for providing the neighborhood-level data; and Semra Tibebu, MPH, for cleaning the individual-level household size variable. These individuals made their contributions as part of their roles as paid employees of Public Health Ontario at the time of the study.
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