## Problem 238 — rank:102

**Title:** Duration of immune memory

**Added binding assumptions (LaTeX):**

```latex
Specify whether later exposure history is externally fixed, an intervention policy or an endogenous observed history; conditioning on future exposure can select on health and behavior. Require protection at the starting time when interpreting $T_M$ as duration, and handle death as a competing event or an explicit censoring assumption. First loss and current protection remain different outcomes when boosting can restore the protective state.
```

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