Persistence of the Immune Response to an Intramuscular Bivalent (GI.1/GII.4) Norovirus Vaccine in Adults

Background: Major global economic and health burdens due to norovirus gastroenteritis could be addressed by an effective vaccine. Methods: 428 adult recipients of various compositions of the norovirus-vaccine candidate, HIL-214, were followed for 5 years, to assess immune responses to its virus-like–particle antigens, GI.1 and GII.4c. Serum antibodies and peripheral-blood antibody-secreting cells (ASCs) were measured. This report focuses on the single-dose 15/50 (µg GI.1/GII.4c) composition, which had been selected for further clinical development. Results: For single-dose 15/50 recipients (N=105), GI.1-specific and GII.4c-specific histoblood-group-antigen–blocking (HBGA) antibodies appeared to have persisted to 5 years, waning from a peak at 4-to-8 weeks, and plateauing above baseline after 3 years. From 3-to-5 years, GI.1-specific GMTs ranged between 53 (95%CI, 40–71) and 60 (95%CI, 46–77; N=69–97) and were approximately 2-fold above the baseline GMT (24 [95%CI, 20–28]; N=105). GII.4c-specific GMTs ranged between 103 (95%CI, 77–138) and 114 (95%CI, 86–152; N=70–97) and were above baseline, but by less than 2-fold (70 [95%CI, 53–92]; N=105). Similar kinetics were observed for pan-Ig titers and ASCs in a subset. Similar kinetics were also observed for HBGA and pan-Ig titers in recipients of other 15/50 dosages. Conclusion: Immune responses to HIL-214 in adults appear to persist for 5 years.