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Association of Age and Pediatric Household Transmission of SARS-CoV-2 Infection

Our take —

Pediatric cases of SARS-CoV-2 have become more prevalent as the pandemic wears on, raising questions about the role this population plays in transmission. This study examined the impact of index case age on the risk of SARS-CoV-2 transmission in Canadian households between June and December 2020. Among households with pediatric SARS-CoV-2 index cases, 27.3% experienced secondary transmission to other household members. Researchers also found that the youngest children (aged 0-3 years) were the most likely to transmit infection, potentially because effective isolation is not feasible due to the basic parenting and care needs for this age group. These findings suggest that children can play a significant role in SARS-CoV-2 transmission, illustrating the importance of non-pharmaceutical interventions (i.e., masks, hand washing) for caregivers and other household members in the setting of pediatric infection. Data from this study preceded the rise of the Delta variant which is more infectious, and thus may underestimate current risks associated with household transmission related to pediatric index cases.

Study design

Retrospective Cohort

Study population and setting

The role of the pediatric population in SARS-CoV-2 transmission remains largely unexplored, in part due to the low proportion of symptomatic cases for this age group. This population-based cohort study examined the role of index case age in household transmission of SARS-CoV-2 in Ontario, Canada between June and December 2020. All data were collected from provincial public health databases. All cases were PCR-confirmed, and onset dates were determined based on timing of initial symptoms or specimen collection date. Index cases were defined as the earliest case in each household; index cases were grouped for analysis into four age categories (0-3, 4-8, 9-13, and 14-17). Secondary cases were defined as those among household members with disease onset 1 to 14 days following the index case. Odds of SARS-CoV-2 transmission according to index case age were determined using logistic regression, with stratified and sensitivity analyses.

Summary of Main Findings

Among 6,280 households with pediatric SARS-CoV-2 index cases (mean index case age = 10.7 years), 1,717 (27.3%) experienced secondary household transmission. Index cases occurred more frequently with increasing age (0-3: 776, 4-8: 1,257, 9-13: 1,881, 14-17 years: 2,376). However, index children between 0 and 3 years of age were more likely to transmit SARS-CoV-2 to other household members (OR: 1.43, CI: 1.17-1.75, compared to the 14-17 year age group), independent of symptomatic vs. asymptomatic infection, school/childcare opening dates, and documented school/childcare outbreaks. This association was maintained in sensitivity analyses, which included alternative secondary case windows (2-14 days, 4-14 days), adjustments for household size, and the inclusion of only symptomatic index cases. 

Study Strengths

Logistic regression models included relevant covariates (gender, household size, etc.), and the large study population allowed for stratified analyses. A python-based algorithm was used to address matching based on natural language, which allowed for more reliable household case grouping. Sensitivity analyses confirmed study results, increasing certainty of their validity.


Secondary cases were assumed to originate from household index cases, but infection could have been acquired in the community; this would result in overestimates of household transmission. COVID-19 database systems evolved during the study period, which could have led to inconsistencies in reporting. Secondary attack rates could not be calculated, because the number of uninfected contacts for the full cohort was unknown. Finally, this study was completed prior to the rise of the Delta variant and does not capture its likely significant impact on household transmission.

Value added

This large, population-based study demonstrated an increased risk for household SARS-CoV-2 transmission by younger vs. older children.

This review was posted on: 1 September 2021