disease-free periodic solution, one obtains a scalar periodic linear delay differential
equation for the infectives, namely [ , (.)], which has exactly the same form as our equation ( .
). Let CP be the Banach space of continuous P-… Figures and show situations when the
stability is just the opposite that one would expect from the sign of r. Overall, our results
show that for a large class of scalar periodic delay differential equations, time averaging of …