Enveloped RNA viruses have evolved mechanisms for surface glycoproteins to evade host immune responses, which exhibit substantial variability, even among different strains. Natural infection and vaccines using native forms of surface proteins may induce broadly neutralizing antibodies, yet with low and ineffective levels. Class I membrane-fusion proteins of enveloped RNA viruses, HIV-1, influenza A virus, SARS-CoV-2, yield a stable conformation (so-called “pre-fusion”) in providing fusion between viral and host cell membranes. Here, ERVW-1 is linked to infection.