March 12, 2007

Vaccine Shows Promise in Preventing Hepatitis E

Image with a large cluster of circular viruses Hepatitis viruses seen by an electron microscopeU.S. Centers for Disease Control and Prevention.

An experimental vaccine appears safe and effective in preventing hepatitis E, a sometimes-deadly viral disease prevalent in developing countries. The genetically engineered vaccine was originally created and tested over the past two decades by scientists at NIH's National Institute of Allergy and Infectious Diseases (NIAID).

Although hepatitis E is relatively rare in the United States, health officials estimate that about one-third of the world's population has been infected with the virus, which is spread mainly through contaminated food and water. Like four other known hepatitis viruses — named A, B, C and D — hepatitis E infects and damages the liver, causing a yellowing of the skin, abdominal cramps, nausea and fever. Most people recover within a few weeks, but hepatitis E poses a particular threat to pregnant women, who have a mortality rate of about 20% if infected during their third trimester.

NIAID's Dr. Robert Purcell and other researchers first identified hepatitis E as a distinct disease in 1980. Purcell and his colleagues later created an experimental vaccine by inserting a gene for a viral coat protein into cultured insect cells, which then mass-produce the protein. The researchers have shown over the past decade that the purified viral protein, administered as an experimental vaccine, can protect nonhuman primates from hepatitis E. A small clinical trial later found the vaccine to be safe and able to trigger an immune response in humans.

These encouraging results prompted scientists to conduct a larger clinical trial involving nearly 2,000 healthy adults in Nepal, where hepatitis E is widespread. This "phase II" trial received primary support from the U.S. Army and GlaxoSmithKline Biologicals, whose scientists are collaborating to develop the vaccine for clinical use.

As reported in the March 1 issue of the New England Journal of Medicine, about half of the study participants received the vaccine in three doses; the other half received placebo. After a follow-up period of about 2 years, the researchers found that the 3-dose vaccine was nearly 96% effective in preventing hepatitis E. Of the 69 volunteers who developed symptoms and were confirmed to have hepatitis E, only three were in the vaccine group. The researchers tested for viral infection only in volunteers who had symptoms of hepatitis, however, so it's possible that subclinical infections remained undetected.

The vaccine also provoked strong immune system responses after each dose. Antibody levels spiked tenfold a month after the third dose and then gradually tapered off. The researchers say the rising responses suggest the presence of immunologic memory that can be protective even though the antibody levels eventually decline. The widely used hepatitis B vaccine is likewise protective even after antibody levels drop.

Because nearly all of the study participants were healthy men over 18 years old, it's not yet clear if the vaccine is safe and effective in other at-risk groups, such as pregnant women or children. Further study will be needed to assess the vaccine's ability to prevent infections in a broader range of the population.

— by Vicki Contie

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