TABLE 1.

Numbers of immunized and control horses which were included in the efficacy study during 2011 and 2012^a

Parameterb	2011c		2012
	IH (WNV seronegative, primo-vaccinated)	CH (WNV seronegative)	IH (WNV seronegative, primo-vaccinated)	IH (primo-vaccinated in 2011 but not infected, received annual booster vaccine dose in 2012)	CH (WNV seronegative of 2011 but not infected + WNV seronegative, selected in 2012)
No. of horses per group	85	33	55	52	33 (21 + 12)
No. (%) of WNV naturally infected horses determined by cELISA and/or SNT	32/85 (38)	12/33 (36)	14/55 (26)	15/52 (29)d	9/33 (27)
No. (%) of WNV naturally infected horses with clinical signs, confirmed by MAC-ELISA	0/32 (0)	1/12 (8)	0/14 (0)	0/15 (0)	2/9 (22)
Total no. (%) of infected horses per year	44/118 (37)		38/140 (27)

^aNumbers and infection rates of horses per year and numbers of horses which exhibited neurological signs due to WNV infection are also included in the table.

^bcELISA, competitive enzyme-linked immunosorbent assay; SNT, serum neutralization test; MAC-ELISA, IgM antibody capture enzyme-linked immunosorbent assay.

^cIH, immunized horses; CH, control horses.

^dIndirect determination.