In Chicago C2-infected rabbits, V5 diversity is not significantly different in rabbits previously immunized with V5-KLH, V6-KLH, or KHL alone, or in unimmunized controls (Panel A). In contrast, V6 variants more readily are seen in rabbits previously immunized with V6-KLH, compared to V5-KLH- or KLH-immunized rabbits or in unimmunized controls (Panel B).