Neutralising antibodies (nAbs) are produced by the humoral immune system to control and prevent viral infection. nAbs specifically recognise and bind to structural components of virus particles and frustrate entry by, for instance, preventing receptor interactions. However, viruses such as HIV and HCV have evolved an array of countermeasures to evade nAbs. Strategies include antigenic variation, direct cell-to-cell transmission and conformational masking of critical epitopes.