Table 4.

Subjects with a 4-fold increase in hemagglutination inhibition titers, in comparison with prevaccination titers.

Prevaccination titer	Subjects with >4-fold response, %	GMT (95% CI)
H3N2 strain
<1:8 (n =23)	82.6a	53.41 (28.89–98.74)c
≥1:8 (n =16)	12.5a	12.88 (8.46–19.62)c
P	<.001	<.001
H1N1 strain
<1:8 (n =23)	65.2a	20.99 (12.93–34.07)c
≥1:8 (n =17)	11.8a	11.09 (6.79–18.09)c
P	<.001	.06
B strain
<1:8 (n =30)	3.3b	4.81 (3.93–5.90)c
≥1:8 (n =10)	0b	9.85 (5.07–19.12)c
P	.99	.04

NOTE. CI, confidence interval; GMT, geometric mean titer.

^aχ² test.

^bFisher’s exact test.

^cTwo-sample t test, assuming unequal variance.