Serum antibody responses to the vaccine containing 50 μg of norovirus GI.1 virus-like particle (VLP) and 50 μg of consensus norovirus GII.4 VLP in 18–49 year olds (cohorts A and D), 50–64 year olds (cohort B), and 65–85 year olds (cohort C). Placebo recipients are combined across all cohorts. Subjects received 2 doses of vaccine separated by 28 days (day 0 and day 28). Geometric mean titers (GMTs) of antibody are shown to GI.1 (A, C, E) and GII.4 consensus (B, D, F) VLPs as assessed by total immunoglobulin (A and B), immunoglobulin G (C and D), and immunoglobulin A (E and F) immunoassays.