A young child died two and a half days after receiving an experimental viral vector designed to deliver genes deep into the brain, according to a STAT+ report. The patient had been treated with a brain‑penetrant viral platform developed by Capsida Biotherapeutics; the death prompted immediate re-evaluation across labs and companies developing similar neurotropic vectors. Researchers and companies are reviewing preclinical tolerability, dosing regimens, and biodistribution data to identify whether the adverse event reflects a product‑specific toxicity or a class risk for brain‑targeting viral carriers. STAT+ reported that investigators and rare‑disease advocates are scrambling to assess program timelines and patient safety monitoring. Regulators and sponsors are closely watching inflammatory, off‑target, and innate immune signals in ongoing trials. The account underscores how a single serious adverse event in a first‑in‑human use of a novel delivery technology can cascade into program holds, new safety requirements, and altered risk–benefit calculations for brain gene therapies.