The study investigates age-dependent effects on the transmission and control of the COVID-19 epidemic. Using an age-structured mathematical model, researchers analyzed data from China, Italy, Japan, Singapore, Canada, and South Korea. They found that individuals under 20 years old have approximately half the susceptibility to SARS-CoV-2 infection compared to adults over 20. Clinical symptoms manifest in 21% of infections in 10- to 19-year-olds, rising to 69% in those over 70. These findings suggest that interventions targeting children may have limited impact on reducing transmission, especially if subclinical infections are not highly transmissible. Age-specific clinical fraction and susceptibility estimates have implications for the global burden of COVID-19, as demographic differences across regions affect expected case numbers. Countries with younger populations may experience lower per capita clinical case rates, though comorbidities in low-income countries could influence disease severity. Without effective control measures, regions with older populations may see disproportionately more cases, particularly in later stages of an unmitigated epidemic. The study also highlights that age-dependent severity and transmission patterns are critical for understanding the impact of social-distancing interventions, especially those targeting schools. Three model variants were used to analyze the relative contributions of age-varying susceptibility, clinical fraction, and contact patterns. The model with age-varying susceptibility and clinical fraction best explained the observed age distribution of cases. The study found that children have lower susceptibility and a lower clinical fraction, but their higher contact rates could lead to increased transmission. School closures were found to be effective in reducing transmission, but their impact varied depending on the infectiousness of subclinical infections. The study also found that the expected global burden of COVID-19 varies by population age structure, with older populations experiencing higher case rates. The findings have implications for public health planning and the effectiveness of control measures in different regions.The study investigates age-dependent effects on the transmission and control of the COVID-19 epidemic. Using an age-structured mathematical model, researchers analyzed data from China, Italy, Japan, Singapore, Canada, and South Korea. They found that individuals under 20 years old have approximately half the susceptibility to SARS-CoV-2 infection compared to adults over 20. Clinical symptoms manifest in 21% of infections in 10- to 19-year-olds, rising to 69% in those over 70. These findings suggest that interventions targeting children may have limited impact on reducing transmission, especially if subclinical infections are not highly transmissible. Age-specific clinical fraction and susceptibility estimates have implications for the global burden of COVID-19, as demographic differences across regions affect expected case numbers. Countries with younger populations may experience lower per capita clinical case rates, though comorbidities in low-income countries could influence disease severity. Without effective control measures, regions with older populations may see disproportionately more cases, particularly in later stages of an unmitigated epidemic. The study also highlights that age-dependent severity and transmission patterns are critical for understanding the impact of social-distancing interventions, especially those targeting schools. Three model variants were used to analyze the relative contributions of age-varying susceptibility, clinical fraction, and contact patterns. The model with age-varying susceptibility and clinical fraction best explained the observed age distribution of cases. The study found that children have lower susceptibility and a lower clinical fraction, but their higher contact rates could lead to increased transmission. School closures were found to be effective in reducing transmission, but their impact varied depending on the infectiousness of subclinical infections. The study also found that the expected global burden of COVID-19 varies by population age structure, with older populations experiencing higher case rates. The findings have implications for public health planning and the effectiveness of control measures in different regions.