Choose Clear and Correct over Concise

1 The decline in CD4 count during HIV-1 infection is not constant over time.

2 The decline in CD4 count during the course of HIV-1 infection is not constant.

Here, there is a potential confusion of an event (i.e. the initial infection), and what occurs after the event (i.e. the progression of the infection over time). The extra phrase makes it clear what is referred to.