https://www.statnews.com/2020/09/09/astrazeneca-covid19-vaccine-trial-hold-patient-report/
Apparently, the trial participant has transverse myelitis (a known vaccine reaction). In typical pharmaceutical sleight of hand a previous case of MS that occurred in association with the vaccine trial has been dismissed as likely not related to the vaccine.
(Despite pharmaceutical company malfeasance "autoimmune" disorders such as MS are relatively common vaccine responses.)