Abstract: The present invention provides an isolated polynucleotide comprising or consisting of the nucleotide sequence encoding the G protein of human respiratory syncytial virus (RSV), wherein the nucleotide sequence is codon optimised for expression in mammalian cells and wherein the polynucleotide provides increased expression of the G protein in mammalian cells relative to expression of the wildtype RSV-G gene. Preferably, the polynucleotide comprises or consists of the nucleotide sequence of SEQ ID NO:2. Further aspects of the invention provide pharmaceutical compositions, in particular vaccines, for use in methods of immunising a subject against RSV infection.