When a time-varying confounder (such as CD4 count in our example, CD41) is affected by previous treatment (AZT0) as in the DAG of Figure 2B, the time-varying confounder (CD41) is also an “intermediate” for the effect of previous treatment (AZT0) on the outcome (progression to AIDS), represented by the path AZT0 → CD41 → AIDS. Here, ITGA2B is linked to AIDS.