Table 5.

Influence of passively transferred H5 antibodies on the serological response of chickens to the commercial H5N1 vaccine

i.p. injection with	HRBC HI GMT*
	Prevac†	4 wpv	3 wpb	2 wpc
PBS	<10 (0/9)	49 (7/9)	86 (9/9)	101 (9/9)
1:100-diluted sera	<10 (0/9)	59 (9/9)	137 (9/9)	209 (9/9)
1:10-diluted sera	<10 (0/9)	31 (8/9)	80 (9/9)	137 (9/9)
Undiluted sera	<10 (0/9)	17 (4/9)	47 (8/9)	49 (7/7)
Control‡	<10 (0/9)	<10 (0/9)	<10 (0/9)	ndd

Prevac, prevaccination; wpv, weeks postvaccination; wpb, weeks postboost; wpc, weeks postchallenge; nd, not determined because of death.

*Boost vaccination with YEBIO H5N1 Re-1 vaccine occurred 4 wk after initial vaccination, and challenge with the lethal Ck/Qal-Egypt/1/08 (H5N1) virus occurred 3 wk later. HI titers against challenge virus (Ck/Qal-Egypt/1/08 [H5N1]) are the reciprocals of the highest dilutions of sera that inhibited hemagglutination by 4 HA units of virus. The results are the geometric mean titers of positive sera (≥10). Values in parentheses are number of chickens with positive sera/total number.

^†The prevaccination samples were collected from 1-wk-old chickens on the day before i.p. injection of H5 antibodies.

^‡Chickens were immunized passively with pooled anti-H5 chicken sera but not vaccinated before challenge.