Live flavivirus vaccines: reasons for caution.
BACKGROUND
Dengue, Japanese encephalitis, tick-borne encephalitis, yellow fever, and West Nile viruses cause substantial morbidity and mortality each year. Modern transportation and the relaxation of mosquito-control measures are largely responsible for the increase of disease caused by flaviviruses. Without effective antiviral drugs, vaccination offers the best chance of decreasing the incidence of these diseases, and live virus vaccines are the most promising and cost effective. However, flaviviruses can recombine, which raises the possibility of recombination between a vaccine strain and wild-type virus resulting in a new virus with potentially undesirable properties.


BACKGROUND
Recently, Arunee Sabchareon and colleagues reported up to 90% seroconversion rates in a phase I trial of live-attenuated dengue-virus vaccines in children (Pediatr Infect Dis J 2004; 23: 99-109). Other live flavivirus vaccines have also been tested against dengue, Japanese encephalitis, and West Nile viruses. Thus far, efficacy seems promising.


CONCLUSIONS
Safety issues with the live flavivirus vaccines need to be recognised and addressed. The theoretical possibility of untoward recombination events can never be entirely dismissed, but steps can be taken to minimise risk. The development of non-live flavivirus vaccines should be encouraged.
Seligman
Stephen J
SJ
Department of Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA. stephen_seligman@nymc.edu
Gould
Ernest A
EA
D020241:Encephalomyelitis, Western Equine / Q000235:genetics; D005416:Flavivirus / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity; D018177:Flavivirus Infections / Q000517:prevention & control / Q000821:virology; D006801:Humans; D011995:Recombination, Genetic; D014613:Vaccines, Attenuated; D014765:Viral Vaccines / Q000009:adverse effects*; D014774:Virulence / Q000235:genetics; D022341:Yellow Fever Vaccine
D014613:Vaccines, Attenuated; D014765:Viral Vaccines; D022341:Yellow Fever Vaccine