The present invention relates to the use of the immortalised cell line ECACC 09070703, deposited on 7 Jul. 2009 at the European Collection of Authenticated Cell Cultures (ECACC, Salisbury, UK) under the number 09070703, for the production of a viral vaccine constituted of an attenuated strain derived from a human metapneumovirus.

The disclosure provides combination mRNA vaccines for respiratory viruses, as well as methods of using the vaccines.