Neutralizing activity of antibodies elicited by Ad26.COV2.S against SARS-CoV-2– spike variants. NHPs received 1 × 10¹¹ vp Ad26.COV2.S in a one-dose regimen (n = 6) or a two-dose regimen of 5 × 10¹⁰ vp Ad26.COV2.S (n = 6) or control Ad26.RSV.gLuc (n = 4) at study weeks 0 and 8. Neutralizing antibody titers of a subset (n = 4 per group) of Ad26.COV2.S-immunized NHP serum samples are shown. Dots are week 8 samples from the one-dose 10¹¹-vp treatment group (i.e., 8 wk after the first dose). Triangles are week 10 samples from the two-dose 5 × 10¹⁰–vp treatment group (i.e., 2 wk after the second dose). Note that serum from one animal from the two-dose 5 × 10¹⁰–vp treatment group was not measured against the B.1 lineage (D614G) + E484K variant and lineage B.1.351 501Y.V2–del242-244 (RSA) due to lack of sufficient volume. Neutralizing antibody titers were below the limit of detection (LOD) in serum from the sham-immunized group, and sera did not have neutralizing antibody titers against the psVNA specificity control (i.e., lentivirus pseudotyped with VSVΔG). Neutralizing antibody titers are expressed as the geometric mean dilution giving a 50% reduction (IC₅₀) in the luciferase readout relative to control wells without any serum added. Individual dots represent individual samples, as a geometric mean of a maximum of four individual assay runs of NHP samples, depending on the variant. Red horizontal bars per SARS-CoV-2–spike variant represent average geometric mean titers of individual NHPs. Dashed horizontal line represents the LOD of a 1:20 dilution. Samples with no measurable titer were set at LOD.