In the mid-1990s, a group of scientists in the NIAID Laboratory of Infectious Diseases (LID) discovered a vaccine for hepatitis E virus (HEV). But the story does not end with their discovery. Nor did it begin when the same group, led by Robert Purcell, M.D., first began working on hepatitis E—a disease responsible for numerous epidemics in Central and Southeast Asia, North and West Africa, and Mexico.
The story really began more than half a century ago—in one of the worst outbreaks of waterborne hepatitis, which struck New Delhi, India, in the winter of 1955–1956.
Monsoon flooding forced the Jamuna River to change directions. It washed through a drainage ditch collecting the city’s sewage, and from there flowed directly into outstretched uptake pipes feeding a treatment plant that supplied drinking water to most of New Delhi. As the dirty floodwaters came into the plant, the chlorination equipment broke. Treatment stopped. But the water kept flowing to the city, and with it, disease.
Monsoon flooding of the Jamuna River caused one of the worst outbreaks of waterborne hepatitis in New Delhi, India, in the winter of 1955–1956. Photo courtesy of Robert Purcell. (Credit: NIAID)
“It was a perfect storm” says Dr. Purcell. “For about a week, raw sewage was running directly into the city’s water supply with no treatment at all.”
By December 1955, New Delhi hospitals were crowded with hepatitis cases. Nobody knew what caused the outbreak, but it was assumed to be hepatitis A virus.
“But that didn’t make sense,” says Dr. Purcell. It was a mystery how hepatitis A could cause such a large outbreak in the first place. Virtually the entire population of New Delhi in those days already had been exposed to the hepatitis A virus as children. These earlier infections should have left them with disease-fighting antibodies that would have prevented them from developing hepatitis, severely limiting the citywide outbreak. Plus the outbreak caused something nobody had ever seen with hepatitis A: the disease had a much higher mortality for women in their third trimester of pregnancy.
The only explanation was that the contamination of the water supply was so great as to overwhelm this immunity and allow people to get the disease—a flimsy argument, but one that stood for the next two decades. In 1980, however, Dr. Purcell and his colleagues showed that these outbreaks were not hepatitis A at all but what was eventually named hepatitis E.
The origins of Dr. Purcell’s discovery of hepatitis E go back to the late 1960s, when his colleague and fellow NIAID investigator Albert Kapikian, M.D., used immune electron microscopy to identify several previously elusive intestinal viruses. Dr. Kapikian used the technique in 1972 to identify the Norwalk virus. One year later he collaborated with Dr. Purcell and Stephen Feinstone, M.D., to identify hepatitis A virus.
Building upon this work, Dr. Purcell and his colleagues had by the late 1970s developed one of the first diagnostic tests and an early vaccine for hepatitis A. Then he read an article by Khorshed Pavri, Ph.D., director of the Institute of Virology in Pune, India. She had been a young research technician during the 1955–1956 outbreak and had collected samples from people with hepatitis. These samples had remained untouched in a freezer since that time.
Shown here are (left to right) Robert Purcell, Albert Kapikian, and Stephen Feinstone with an electron microscope. (Credit: NIAID)
Dr. Purcell contacted her immediately, and she sent some of her frozen samples to Bethesda, Maryland. Together, they showed that the outbreak victims were not infected with hepatitis A virus. “We knew it was probably a new virus,” says Purcell, but not knowing which exact virus it was, they dubbed it "epidemic non-A, non-B" hepatitis virus—later renamed hepatitis E. Simultaneously, a group in India led by Mohammed Sultan Khuroo, M.D., made the same determination.
Neither group was able to visualize HEV under the microscope, though. Doing so required obtaining large quantities of the virus, which neither of them had. So it fell to a Soviet virologist named Mikhail Balayan, M.D., whose self sacrifice bordered on the extreme.
In 1983, Dr. Balayan was investigating an outbreak of non-A, non-B hepatitis in a central Asian part of the Soviet Union. Though he wanted to bring samples back to his Moscow laboratory, he lacked refrigeration. So he made a shake of yogurt and an infected patient’s stool, drank it, went back to Moscow, and waited. When he became seriously ill a few weeks later, he started collecting and analyzing his own samples. In these he found a new virus that produced liver injury in laboratory animals and could be seen by electron microscopy. It looked a lot like hepatitis A virus, but he could show that it was not, because he already had antibodies against the hepatitis A virus and these did not react with the new virus.
Hepatitis E virus infection - Hepatitis E virus is acquired from contaminated food or water. Typical symptoms include acute nausea, vomiting, diarrhea, and jaundice. Most people recover from the disease after a few months. Hepatitis E can be deadly, however, especially for women in their third trimester of pregnancy. (Credit: NIAID)
Subsequently, in 1990, Gregory Reyes, Ph.D., and his colleagues at GeneLabs, Inc., cloned and sequenced the genome of the virus in collaboration with Daniel Bradley and colleagues from the Centers for Disease Control and Prevention (CDC). The virus was renamed hepatitis E virus.
After the Soviet Union broke apart in the early 1990s, a number of former Soviet scientists immigrated to the United States. Among them was Sergei Tsarev, Ph.D., who had been one of Dr. Balayan’s collaborators. Dr. Tsarev started working in LID on an antibody test to detect HEV in the bloodstream. Together, he and Dr. Purcell found something much more powerful.
There was a lot of excitement over hepatitis vaccines in the early 1990s. The Food and Drug Administration (FDA) had approved the first hepatitis B vaccine in 1982 and the first genetically engineered hepatitis B vaccine in 1987. Clinical trials of the first vaccine for hepatitis A also looked promising, and FDA approved the first hepatitis A vaccine in 1995. The question on many people’s minds in the early 1990s was, Would a vaccine for hepatitis E be next?
The first step toward making a vaccine came while Dr. Tsarev was looking for various ways to generate HEV proteins in the test tube. His colleague in LID, Suzanne Emerson, Ph.D., suggested he try a new method involving insect cells and an insect virus called a baculovirus. By chance, when he grew one particular HEV protein this way, the protein was processed by enzymes encoded by the insect cells or the baculovirus, resulting in something that could be used as a vaccine.
“We showed that you could use this vaccine to immunize and protect against several strains of HEV in animals,” says Dr. Purcell.
The story did not end there, of course. The vaccine still needed to be tested in humans.
So NIAID established a collaboration with SmithKline Beecham Biologicals, now GlaxoSmithKline Biologicals, which sponsored production of several pilot lots of recombinant hepatitis E vaccine using NIAID technology. These lots underwent additional testing in animals by NIAID and, ultimately, in clinical trials of the vaccine.
Like NIAID, the U.S. Army Medical Research and Materiel Command’s Walter Reed Army Institute of Research had a longstanding interest in vaccines against viral hepatitis and had worked with NIAID and GlaxoSmithKline Biologicals on development of a hepatitis A vaccine. Under a separate agreement with GlaxoSmithKline Biologicals, the U.S. Army agreed to collaborate on clinical development of the hepatitis E vaccine.
Walter Reed conducted an initial clinical trial of the hepatitis E vaccine in healthy adults in the United States and then a second trial in healthy adults in Kathmandu, Nepal, where hepatitis E is prevalent. After evaluating the data from both trials, the U.S. Army, NIAID, and GlaxoSmithKline Biologicals agreed to conduct a larger clinical trial to confirm that the investigational hepatitis E vaccine conferred protection against hepatitis E disease.
The vaccine efficacy trial took place in Nepal from 2000 to 2004 in collaboration with the Nepalese Army. Though the trial proved difficult, it was successfully completed, and the results appeared in the New England Journal of Medicine.
Read the related story: Hepatitis E Vaccine: A Time of Testing
In the end, the vaccine proved to be safe and highly effective: three doses were 96 percent effective, and two doses 87 percent effective at preventing the disease.
The story of the HEV vaccine is like a three-act play. In the first act, Dr. Purcell and his colleagues identified the “new” disease and later developed a vaccine candidate. The second act, set in Nepal, is where the clinical trial proved the efficacy of the vaccine candidate. The third act, wherein the hepatitis E vaccine candidate is licensed as a vaccine and ultimately is administered to people as part of routine program of disease control in countries like Nepal, is not yet written.
As challenging as the vaccine efficacy trial was, perhaps the hardest work is still ahead, notes Dr. Purcell. Many technical questions remain unanswered before licensure. How easy will it be to make large quantities of the vaccine? How should it be formulated for children? Would it be possible to require fewer than three doses? Can HEV vaccine be combined with other vaccines?
There are also larger public health questions involved. What is the burden of disease for hepatitis E in different countries around the world? How large a burden does a country need for it to make sense to implement a widespread vaccination program?
And of course, one of the biggest questions is, Who will pay for the vaccines and how?
“We showed that there is an effective way to prevent this disease,” says GlaxoSmithKline’s Bruce Innis, M.D., one of the leaders of the team formed to conduct clinical trials. “We are seeking public-sector partners who are committed to the long and challenging endeavor to add hepatitis E vaccine to immunization programs in countries where this is needed.”
Shrestha MP et al. Safety and efficacy of a recombinant hepatitis E vaccine. N Engl J Med 356(9):895-903 (2007).
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Last Updated August 30, 2007