The present invention relates to an isolated immunogenic peptide comprising a V2 loop fragment from HIV surface envelope glycoprotein gp120. This peptide binds specifically with antibodies in blood of patients vaccinated with a vaccine that has shown protection from HIV-1 infection, does not react with blood of matched patients who did not receive the vaccine, and can, therefore, elicit anti-HIV-1 antibodies which protect against HIV-1 infection. Other aspects of the present invention relate to an isolated immunogenic polypeptide comprising the peptide inserted into an immunogenic scaffold protein, a vaccine composition comprised of the immunogenic peptide and an immunologically or pharmaceutically acceptable vehicle or excipient as well as methods of inducing an immune response against HIV-1 and methods of detecting HIV-1.