Norovirus is the leading cause of acute viral gastroenteritis in all age groups in the U.S. Each year, on average, norovirus causes 19 to 21 million cases of acute gastroenteritis and leads to 56,000 to 71,000 hospitalizations and 570 to 800 deaths, mostly among young children and older adults. Typical symptoms include dehydration, vomiting, diarrhea with abdominal cramps and nausea. In a study conducted by the University of Pittsburgh and the U.S. Centers for Disease Control and Prevention (CDC) in 2012, the total economic burden of norovirus in the U.S. was estimated at $5.5 billion.
Norovirus is considered one of the most infectious foodborne pathogens given its low infectious dose and resistance to nearly every common sanitization process used in food production. Contamination of cruise ships is particularly well described in the popular press. However, anywhere in closed quarter, such as in U.S. military populations, gastroenteritis outbreaks are reported at rates nearly 10 times that of cruise ships. Additional at-risk populations include hospitalized patients, healthcare workers, food handlers, farm workers and travel industry professionals. There is currently no vaccine to protect against norovirus.
Vaxart is developing a bivalent tablet vaccine for norovirus, a leading cause of acute viral gastroenteritis and food-borne disease in the U.S. and Europe. Because norovirus is a pathogen that infects the small intestine, Vaxart believes a vaccine that produces mucosal antibodies locally in the intestine, in addition to systemic antibodies that circulate in the blood, may better protect against norovirus infection than an injectable vaccine.
Vaxart has completed two Phase 1 clinical trials with its monovalent oral tablet vaccine based on the GI.1 norovirus strain, demonstrating its norovirus tablet vaccine was well tolerated and generated broad systemic and mucosal immune responses. In the recently completed clinical Phase 1b dose-optimization study in healthy adults, in which Vaxart evaluated four different dosing regimens, all vaccine recipients (100%) in the high-dose group responded as measured by a significant increase in norovirus specific B cells of both IgA and IgG subtypes. In the same group, there was at least a two-fold increase of norovirus specific antibody titers in serum in more than 90% of recipients 56 days after dosing.
In a Phase 1 trial of its bivalent norovirus vaccine designed to assess safety and immunogenicity there were not significant differences in the adverse event rates to placebo. The IgA ASC response rates of 90-93% for GII.4 and 78-86% for GI.1 showed no interference between genotypes in the bivalent arm versus the monovalent arms of the study.