After a catalyst passes, implied volatility collapses (the vol crush) — and in a short-vanna regime, that falling IV forces dealers to buy, sparking a bounce or rally. It links two concepts most traders learn separately.

The two-step mechanism

Step 1 — the crush: before an event (FOMC, CPI), IV is elevated pricing the uncertainty; once the event passes and uncertainty resolves, IV collapses. Step 2 — the vanna response: that falling IV changes dealers’ deltas via vanna, and in the common short-vanna setup they must buy to re-hedge — lifting price (a post-event bounce).

Why it’s self-reinforcing

The buying calms vol further, which forces more vanna buying — a loop that can turn a relief bounce into a sustained vanna rally. It’s why markets so often rally after a feared event even when the news wasn’t especially good: the mechanical vol-crush-to-vanna flow does the lifting.

The scare passing is bullish not because the news was good, but because the fear premium deflating forces dealers to buy. Vol crush is the fuse; vanna is the rocket.

What it means for a scalper

Expect a potential vanna bounce after a feared catalyst resolves with IV collapsing — don’t reflexively fade the relief rally, since it’s mechanically supported. Recognize the setup (event passed, VIX dropping) and respect the upward bias. It’s one of the cleaner dealer-flow patterns to know.