Incidence of Yellow Fever Vaccine-Associated Neurotropic Disease

Although the yellow fever 17D strain live-attenuated vaccine has been widely used over the past seven decades with a long history of safe records, recent reports of serious, sometimes fatal, adverse events, raised concerns about its tolerance. We extracted all cases of serious neurologic adverse events that occurred within 30 days of yellow fever vaccination in our institution during 2000-2008. Four cases (meningitis, n = 2 and meningo-encephalitis, n = 2) were identified. The male:female ratio was 3:1, and ages ranged from 21 to 55 years. Cerebrospinal fluid examination showed pleocytosis (10-82 cells/mm(3), 64-84% lymphocytes), with slightly elevated protein levels (0.4-0.68 g/L). All symptoms resolved in three patients, but attention disorder and cerebellar syndrome persisted in one patient (at six months follow-up). The incidence of yellow fever vaccine-associated serious neurologic events was estimated to be 9.9/100,000 vaccine doses (95% confidence interval = 2.7-25.4/1.00,000) in this study, which was 10 times higher than previous estimates that did not include acute meningitis.