Yellow fever vaccine safety Cases of viscerotropic disease
following yellow fever vaccination were described in the United
States and other countries, and current evidence suggests that
these cases were a result of vaccine-type virus and not of
reversion of the vaccine virus to wild type. Unlike the
viscerotropic complications of yellow fever vaccination,
reported neurotropic cases from the United States have not been
fatal. The neurotropic cases presented as GBS (thought to be
immunemediated), encephalopathy (thought to be due to active
invasion of the central nervous system by the virus) or acute
demyelinating encephalomyelitis (thought to be caused either by
direct invasion of the brain by the virus or by an immune-
mediated response to the virus). All cases of viscerotropic
disease to date have been reported in primary vaccinees,
starting 2–5 days after vaccination. Whether this reflects the
persistence of pre-existing immunity at the time of
revaccination or lower rates of revaccination in the study popul