Surprisingly, we found that regardless of prior vaccination, 14 of 22 (64%) SHIV.5MUT-infected macaques developed potent V3-glycan bNAb responses within one year of infection in contrast to 0 of 14 (0%) control animals infected with SHIV.BG505.N332, despite differing by only four residues in the V1 region of Env (p<0.0001, Fisher’s exact test). Here, ERVW-1 is linked to infection.