show Abstracthide AbstractLassa fever virus is a Category A zoonotic pathogen that infects rodents and is occasionally transmitted to humans with fatal results. Following a pilot experiment to establish the optimal library construction method, we propose to sequence 26 viral isolates derived from passages of an attenuated re-assorted Lassa vaccine candidate strain (Mopeia-Lassa 29 or ML29) in mice and non-human primates. This will allow the in vivo variation of this vaccine strain to be assessed. Lassa virus has a bi-segmented, single-stranded RNA genome; the ML29 vaccine candidate is a re-assorted virus containing the large (L) genomic segment from the non-pathogenic Mopeia virus and the small (S) segment from Lassa virus. The large genomic segment is 7.2 kb, and the small segment is 3.4 kb, for a total genome size of 10.5kb.