Table 2.

Passage history, FCS deletion levels and in vivo outcomes of Victoria 01 stocks.

Cell line used	Passage number				Model species
	1	2	3	4	Hamster	Ferret	Primates
Vero/hSLAM	<1%a	<1%a	<1%a	<1%a	10–20% weight lossb	High viral loadsc	High viral loadsc

^aNo deletions detected in over 99% of the reads spanning the FCS region.

^bNational Institute for Biological Standards and Control (NIBSC) and PHE data independently obtain this outcome.

^cFor the purposes of this article, high viral load is characterized as viral RNA titres at or above 1.0E+07 RNA copies/ml in nasal passage or lung samples and low viral load is characterized as below that concentration.