Proxy immunization enabling yellow fever vaccination after thymectomy.

Yellow fever (YF) vaccination is generally contraindicated in individuals with thymic disorders because of the risk of YF vaccine-associated viscerotropic disease (YEL‑AVD). As YF transmission expands and global travel increases, protection may still be indicated for selected patients with prior thymectomy. We report a 25‑year‑old woman with childhood thymectomy for acetylcholine receptor antibody-positive generalized myasthenia gravis, now in long‑term remission without immunosuppression, who required YF prevention. Immune competence was evaluated using monitored orthoflaviviral proxy immunization with the live‑attenuated tetravalent dengue vaccine (TAK‑003). She experienced mild reactogenicity and developed dengue‑specific antibodies and T‑cell responses, with preserved B-cell maturation. After confirming orthoflaviviral immune competence, she received YF‑17D‑204 vaccination, which was well tolerated and induced transient viremia, seroconversion, and functional YF‑specific B‑ and T‑cell responses. This case demonstrates the feasibility of an individualized, immune‑guided approach to safely administering YF vaccination after thymectomy and highlights the need for broader clinical confirmation.