Although these reports call into question the safety of yellow fever vaccination, the overall conclusion to be drawn is that vaccination programs should be continued.
However, there is the need for new research to explain how some individuals can become sensitized to yellow fever vaccine.
The vaccine is generally regarded as one of the safest virus vaccines, with few side-effects or adverse events.
Pedro Vasconcelos and colleagues, from the WHO Collaborating Center for Arbovirus Reference and Research, Brazil, report the occurrence of two fatal cases of hemorrhagic fever associated with yellow fever 17DD sub-strain vaccine.
The first case was a 5-year-old white girl. Clinical presentation was characterized by sudden onset of fever, accompanied by headache, malaise, and vomiting 3 days after receiving yellow fever and measles-mumps-rubella vaccines. She died after a 5-day illness.
The second patient was a 22-year-old Afro-Caribbean woman. She developed a sore throat and fever, accompanied by headache, myalgia, nausea, and vomiting 4 days after yellow-fever vaccination. She then developed symptoms including jaundice and renal failure, and died after 6 days of illness.
Tissue damage in both patients was typical of wild-type yellow fever.
The investigators conclude that, although these serious complications of yellow-fever vaccination are extremely rare, the safety of yellow fever 17DD vaccine needs to be reviewed.
|Safety of yellow fever vaccine needs to be investigated.|
In the second report, Michael Martin and colleagues from the Centers for Disease Control, Atlanta, USA, describe the illness (and death in 3 cases) of 4 elderly patients shortly after they had been vaccinated against yellow fever.
The patients developed fever, myalgia, headache, and confusion, followed by severe multi-systemic illnesses.
The investigators suggest that there may be a possible causal relation between the illnesses and yellow-fever vaccination.
However, they caution that because yellow fever remains an important cause of illness and death in South America and Africa, vaccination should be maintained until the frequency of adverse events to vaccination is quantified.
Raymond Chan and colleagues from the South Western Area Pathology Service, Sydney, Australia, describe, in a research letter, a man vaccinated with the 17D204 strain of yellow fever virus, who later died of the disease.
Genetic sequencing showed that the virus isolated from the patient was identical to the vaccine strain of the same batch, but differed from wild-type virus.
Both viruses contained a mutation, although the association of this mutation with virulence is unknown.
The investigators comment that severe, rapidly progressive, and ultimately fatal disease can follow use of the 17D204-vaccine strain.
There is also need for renewed discussion as to the safety of the vaccine and the indications for its use.
In an accompanying Commentary, Philippe Marianneau and colleagues from Institut Pasteur, Lyons, France, conclude, "The use of 17D vaccination remains highly advisable for people living in or travelling to endemic and epidemic zones.
"However, these three reports raise relevant questions about the mechanisms of attenuation of yellow-fever virus that should be urgently investigated."