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SAN FRANCISCO – An investigational norovirus vaccine safely reduced the vomiting and diarrhea associated with norovirus genotype GII.4, the most common strain of the disease, in a randomized, double-blind, placebo-controlled trial.
Study subjects were randomized to receive either placebo or the bivalent vaccine, which also targets norovirus genotype GI.1 (the Norwalk strain), and they subsequently drank water containing a significant amount of the GII.4 strain of the virus. Infection with the challenge virus occurred in 52% of 56 subjects in the vaccine group and 60.4% of 53 subjects in the placebo group. Significantly fewer patients with infection in the vaccine group, compared with the placebo group, reported severe vomiting and/or diarrhea (0% vs. 8.3%), moderate or severe diarrhea or vomiting (6.0% vs. 18.8%), and vomiting and/or diarrhea of any severity (20.0% vs. 41.7%), Dr. David I. Bernstein reported during a press conference at an annual scientific meeting on infectious diseases.
Also, fewer subjects in the vaccine group shed norovirus at day 10 after the challenge (22.4% vs. 36.2%), according to Dr. Bernstein of Cincinnati Children’s Hospital Medical Center and the University of Cincinnati.
Participants in this multicenter trial were adults aged 18-50 years who were injected twice, 28 days apart, with either placebo or the vaccine – a virus-like particle vaccine adjuvanted with monophosphoryl lipid A (MPL) and alum. The virus challenge included 4,000 real-time polymerase chain reaction genome equivalents of a heterologous GII.4 norovirus. Subjects were isolated for 4 days as inpatients following the challenge, during which time they were monitored for infection.
"We are excited about the results," Dr. Bernstein said, noting that the findings with respect to the effect on severe symptoms are particularly encouraging because it is severe disease that is of the most concern.
Larger trials in a real-world setting are planned, he said.
Norovirus is the leading cause of acute gastroenteritis among both adults and children, and it is highly contagious. Significant outbreaks occur in many settings where people are in close quarters, including health care facilities, child care centers, cruise ships, and in the military, he said.
In fact, 19-21 million Americans are infected each year, and as many as 800 die from the infection. Children and older adults are particularly vulnerable to developing more serious illness.
"Until recently we accepted [norovirus] as a part of life, but this research gives us a glimmer as to a very different future," said Dr. Andrew T. Pavia of the University of Utah, Salt Lake City, the press conference moderator.
Indeed, one could envision a scenario in which this vaccine, if ultimately approved, could be used to help prevent norovirus among nursing home residents, members of the military, cruise ship passengers, and children in school settings, Dr. Bernstein said at the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society.
"This [research] is a good start," he said, adding that there is still a long way to go.
If this vaccine proves as safe and effective in the real world as in the challenge setting used in this trial, it would be a minimum of 5 years before a commercial vaccine was available, he estimated.
Dr. Bernstein reporting serving as an investigator for and receiving research support from LigoCyte Inc., the maker of the investigational vaccine. He also receives royalties for a different norovirus vaccine.
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