Table 1 . Relative fitnesses of wild-type and escape epitopes before and after peak viremia.

Peak viremia	Wild-type epitope	Escape epitopea
Before	1	1 – φ
After	1	(1 – φ)/(1 – c)

^aφ is the cost of escape equivalent to the proportion of cells infected by virus carrying the escape mutation that die before viral reproduction, and c is the proportion of infected cells killed by a CD8⁺ T cell response targeting the epitope.