26 April 2011
Herpes vaccine hamstrung by African strains of virus
by George Atkinson
Harvard Medical School Researchers working on a herpes vaccine say that strains of genital herpes in Africa are far more virulent than those in the United States.
Identification of the properties of the African viruses would open the door to developing a better vaccine, research leader David M. Knipe says. At present, the vaccine farthest along in development (it is headed for clinical trials in about a year) works best against the U.S. strains of herpes simplex 2, but it also protects laboratory animals from the African strains if given in very high doses.
In southern Africa, infection rates among adults for genital herpes are exceedingly high - around 80-90 percent, compared to slightly less than 20 percent in the United States.
According to Knipe, animal tests demonstrate clearly that the strains of herpes virus seen in sub-Saharan Africa are more virulent than the herpes simplex 2 virus strains seen in the United States. That difference suggests that an effective vaccine will probably have to be given to people in Africa in larger or more frequent doses.
Part of the promise of a herpes vaccine is that it can help reduce the impact of HIV/AIDS in southern Africa. Epidemiological studies have shown that genital herpes infection is associated with a three-fold increase in the risk of HIV infection. "If the rate of herpes infection can be reduced, it's conceivable the rate of HIV/AIDS infection will also come down, perhaps reducing the death rate," says Knipe.
Knipe's approach to vaccine development is based on using abnormal, live, mutant viruses to stimulate protective immune responses. These disabled viruses cannot multiply inside cells or cause symptomatic disease, but they do contain enough of the right proteins and molecules needed to arouse detection by a healthy immune system.
Although it has been difficult to create a vaccine for genital herpes, vaccines against a closely related herpes virus - varicella zoster virus, the cause of chicken pox and shingles - proved successful and are now widely used. This gives reason for optimism about a genital herpes vaccine.
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Source: Harvard Medical School