Antibodies with high neutralizing capacity, binding titers, and avidity prechallenge are associated with protection from SHIV infection. The animals were divided into protected and infected groups on the basis of the peak viral load (<2.7 and ≥4.0, respectively). Significant differences between groups were observed with respect to NAb titer, total Ab titer, and avidity. Avidity, total Abs, and Ab ratio are as described in footnotes to Table (footnote c, a, and b, respectively). V1 and V3 NAbs are as described in the legend to Fig. . P values were obtained by the Mann-Whitney test.