Predicted under various transmission-cohort scenarios.

The color gradient changes from purple to blue to reflect R₀ shifting from < 1 to > 1 in each ternary plot, with the white line denoting the boundary. Yellow is used to represent R₀ > 6. (A-C) Assuming child-adult and adult-child transmission rates are identical (black axis), movement along the blue axis indicates that child-child transmission has a weak effect on R₀ at a fixed scale for β₀. (D-F) Fixing child-child transmission to be weak (β₁₁ = 0.1) relative to other interactions, both child-adult and adult-adult transmission play dominant roles in increasing R₀. (G-I) Fixing adult-adult transmission to be weak (β₂₂ = 0.1), only child-adult transmission plays a dominant role in increasing R₀.