Table 2. Summary of evidence base of transmission by children, by study design.

Study design, references	Setting	Main findings
Household cluster studies (25– 27, e24)	Proportion of pediatric index cases and secondary infections versus adult or H5N1 index cases	– Child was rarely index case and rarely caused secondary cases – Different from influenza – Children had lower relative infectivity
School outbreak investigations (28– 30)	High schools and primary schools; staff/student cases; PCR or seroprevalence in close contacts	– Primary school student and staff cases associated with few secondary cases – Older student and staff cases associated with no secondary cases – Sero-positivity in older students: 38.3%, teachers: 43.4%, staff: 59.3%; but much lower in household contacts – Irish cases each exposed 125–475 children and 25–28 adults at school
Sero-prevalence (31– 33, e27)	Population samples;residual clinical samples	– Geneva: In 455 children ages 5–19: 6% sero-positivity vs 8.5% in adults – Spain: 2.9% seropositive among 5–9 yo children vs 5.2% overall; lower in younger children
Clinical laboratory, viral load studies (34, 35)	RT-PCR and cell culture from symptomatic children	Cultivable SARS-CoV-2 in naso-pharyngeal specimens from 52% of 23 symptomatic children
Time-series (e28)	Comparative analysis of school-closures/re-openings; effect on growth rates daily hospitalizations or confirmed cases	– No increased transmission from school-reopening amidst low community transmission, nor from partial return of younger groups amidst higher transmission – No increased staff cases, but increased student cases on return, especially older students (Germany)
Modeling study (36– 38)	Epidemiological modeling school closures/re-opening; assumptions on susceptibility, contact and infectiousness	– Intervention consistently decreases number of cases and delays epidemic – Limited impact of school closures, – Impact lower compared to influenza

Abbreviation: yo = “years old”