An oral norovirus vaccine tablet was safe and elicited mucosal immunity in older adults in a phase 1b clinical trial

Norovirus is a leading cause of acute gastroenteritis globally, with infections in older adults associated with heightened severity and increased risk of mortality. Currently, no licensed vaccines are available to prevent norovirus infection. We developed an orally administered vaccine tablet (VXA-G1.1-NN) that delivers a nonreplicating adenoviral vector expressing norovirus GI.1 major capsid protein VP1 to the small intestine. Here, we report safety and immunogenicity results of a randomized, double-blind, placebo-controlled clinical trial (NCT04854746) that investigated the oral administration of VXA-G1.1-NN in two groups of healthy older adults aged 55 to 65 and 66 to 80 years. VXA-G1.1-NN was administered orally at three dose levels by prime and boost, 28 days apart. Immunization was well tolerated regardless of dose, with mild to moderate reported solicited symptoms and no related serious or grade 3 adverse events. Oral delivery of VXA-G1.1-NN elicited VP1-specific serum immunoglobulin G (IgG) and IgA and functional antibodies in a dose-dependent manner 28 days postvaccination and remained above baseline for 210 days. Moreover, robust circulating VP1-specific IgA antibody-secreting cells were detected 1 week postvaccination along with IgA⁺ plasmablasts expressing the mucosal-homing marker α4β7. VP1-specific IgA increased in saliva and nasal lining fluid 28 days postvaccination in both age groups and remained above baseline concentrations through 210 days, demonstrating durable mucosal responses. This clinical trial established that oral administration of VXA-G1.1-NN is safe, well tolerated, and induces robust systemic and mucosal immune responses in adults up to 80 years old.