This subset of 139 Env-pseudotyped viruses was classified into three groups according to time of infection where sequential gain of HIV-1 antibody responses was used as a marker of time from infection [50]: pre-seroconversion group (n = 58) (no detectable antibodies Ab-; estimated infection <15 days); indeterminate group (n = 26) (evolving antibody responses Ab+/-, estimated infection <37 days); and early post-seroconversion group (n = 55) (near/full seroconversion Ab+; estimated duration of infection < 100 days). This evidence concerns the gene ERVW-1 and infection.