Table 1.

CDC's YFVS Working Group case definition for YEL-AND.⁶

Case ascertainment
Level 1: neurological disease	Level 2: neurotropic disease
Fever (≥100.5°F (>38.1°C) for >24 hours) and headache (>24 hours)	Level 1 neurological disease, and one or more of the following:
Focal neurological dysfunction (including but not limited to ataxia, aphasia and paresis)	Neuroimaging consistent with inflammation (with or without demyelination)
Mental status change (confusion, lethargy, or personality change lasting >24 hours)	EEG finding consistent with encephalopathy
New onset seizure or recurrence of previously controlled seizures
Cerebrospinal fluid (CSF) pleocytosis (>5 WCC/mm)
Elevated CSF protein (>1.5 times the normal limit)
Case definitions
Suspect neurotropic disease
Onset of symptoms and signs occurs within 1–30 days of vaccination with yellow fever vaccine, either given alone or in combination with other vaccinations;
Level 2 neurotropic disease; and no evidence of other diagnoses
Probable neurotropic disease
Suspect YEL-AND, and one or more of the following:
Vaccine-type yellow fever viral isolation from blood (>7 days postvaccination)
Yellow fever 17D§ virus concentration in serum on any day exceeds 3 log10 pfu/mL
Definite neurotropic disease
Suspect YEL-AND, and one or more of the following:
YF-specific CSF IgM
Yellow fever 17D§ virus isolation from CSF
Amplification of vaccine type virus§ from CSF

CDC, Centers for Disease Control and Prevention; YEL-AND, vaccine-associated neurological disease; YF, yellow fever; YFVS, Yellow Fever Vaccine Safety; WCC, white cell count.