Vaxart, Inc. announced top-line data from the Phase 2 challenge study of its oral tablet monovalent norovirus vaccine candidate (NCT05212168). The Phase 2 challenge study enrolled 165 healthy adults, who were randomized 1:1 to receive Vaxart?s monovalent oral tablet vaccine targeting the norovirus GI.1 genotype or placebo. Four weeks after vaccination, subjects were challenged with GI.1 norovirus.

The study achieved its primary endpoints of a statistically significant 29% reduction in the rate of norovirus infection between the vaccinated and placebo arms through Day 8 post challenge, a strong induction of norovirus-specific immunoglobulin A (IgA) and immunoglobulin G (IgG) antibodies, and other immune response endpoints. Vaccination also led to a reduction in norovirus AGE in the vaccine arm compared to placebo, but this was not statistically significant. In a prespecified analysis, the study also showed an 85% decrease in viral shedding in the vaccine arm compared with placebo.

Norovirus is the leading cause of acute viral gastroenteritis in all age groups in the U.S. However, there are no approved vaccines for noroviruses. In the U.S. alone, the annual disease burden from norovirus is $10.6 billion, as on average norovirus causes 19 to 21 million cases of AGE, infects 15% of all children under the age of 5, and leads to 465,000 emergency department visits, 109,000 hospitalizations and 900 deaths. Vaxart believes the reduction in the rate of infection and increases in multiple immunologic endpoints in this challenge study support the potential for its norovirus vaccine program to provide significant public health benefit.

The Company also believes that the numeric reduction in rate of AGE, while not statistically significant, is encouraging, especially given the high dose of challenge virus used in the study, compared with what would occur in a natural infection. Vaxart is currently conducting additional analyses of the data from this challenge study and its prior norovirus trials with the objectives of defining the timing of a larger phase 2b study, and identifying ways to reduce the size and duration of a subsequent Phase 3 registration study.