Table 3.

Pre- and post-TIV immunization HI titers and seroprotection or seroversion rates to H1N1, H3N2, and B vaccine strains in subjects without ILI and in influenza or ILI cases.

HI antibody responses	Subjects with no ILI (n = 52)	ILI cases (n = 19)	Influenza cases (n = 11)	p values
H1N1
Pre-vaccination titersa	179±2.2	151±2.5	144±2.3	.17*
Post-vaccination titersa	378±2.3	274±2.4	195±2.3	.05*
Pre- vs. post- p valuesb	.001	.05	.13	.74**
Seroprotection ratesc	98%	89%	91%	ND
Seroconversion ratesd	10%	0	0
H3N2
Pre-vaccination titersa	289±2.4	268±2.4	230±2.3	.16*
Post-vaccination titersa	468±2.7	389±2.6	301±2.7	.04*
Pre- vs. post- p valuesb	.01	.05	.09	.43**
Seroprotection ratesc	96%	84%%	91%	ND
Seroconversion ratesd	15%	5%	0%
B
Pre-vaccination titersa	79±1.3	76±1.3	64±1.5	.19*
Post-vaccination titersa	87±1.5	82±1.5	66±1.4	.07*
Pre- vs. post- p valuesb	.04	.08	.41	.89**
Seroprotection ratesc	83%	89%	82%	ND
Seroconversion ratesd	2%	0	0

ND: not done.

^*These p values derived from Jonckheere–Terpstra trend tests across participants with no ILI, ILI cases, and serologically confirmed influenza cases.

^**These p values derived from Fisher exact test between subjects with no ILI and influenza cases.

^aMean±geometric SD of geometric mean titers (GMT).

^bThese p values derived from paired t tests of the pre–post immunization difference in log transformed HI titers.

^cSeroprotection defined by post-vaccination HI titer≥1:40.

^dSeroconversion defined by 4-fold or higher HI titer increase after TIV immunization or post- over pre-vaccination HI titer ratio ≥4.