## Problem 207 — rank:286

**Title:** Vaccine-waning function

**Added binding assumptions (LaTeX):**

```latex
Standardized hazard ratios compare treatment-specific survivor risk sets and need not equal a causal cumulative-risk reduction. State whether the target is that hazard-based estimand or a standardized counterfactual risk, and retain the corresponding censoring and survival-selection assumptions. Calendar date, index date and elapsed time satisfy a deterministic relation, so separate waning estimation requires genuine overlapping assignment cohorts rather than a freely varied three-dimensional covariate grid.
```

**Direct edits:** 0. **Fresh external checks:** None; supplied sources retained as provenance.