This disclosure relates to the field of preventing or treating virus infection, in particular, the disclosure relates to agents for vaccination against virus infection and inducing effective virus antigen-specific immune responses such as antibody and/or T cell responses and methods for generating and using such agents. Administration of agents such as RNA disclosed herein to a subject can protect the subject against virus infection. Specifically, the present disclosure relates to amino acid sequences comprising at least a portion of a virus protein having amino acid modifications found in other variants of the virus protein. Administration of RNA encoding one or more of the amino acid sequences may provide protection against diverse virus variants. Methods and agents described herein are, in particular, useful for the prevention or treatment of coronavirus infection such as SARS-CoV-2 infection.