Table 4.

Estimated Absolute and Relative Efficacies of the Inactivated Influenza Vaccine and the Live Attenuated Influenza Vaccine during the 2004–2005 Influenza Season in Michigan.^*

Laboratory-Confirmed Symptomatic Influenza	Cumulative Incidence of Influenza			Relative Risk (95% CI)			Percent Relative Reduction (95% CI)
	Inactivated Vaccine (N = 522)	Live Attenuated Vaccine (N = 519)	Placebo (N = 206)	Inactivated Vaccine vs. Placebo	Live Attenuated Vaccine vs. Placebo	Inactivated vs. Live Attenuated Vaccine	Inactivated Vaccine vs. Placebo	Live Attenuated Vaccine vs. Placebo	Inactivated vs. Live Attenuated Vaccine
	no. of participants (%)
Culture positive	7 (1.3)	13 (2.5)	12 (5.8)	0.23 (0.08 to 0.63)	0.43 (0.18 to 1.03)	0.54 (0.18 to 1.44)	77 (37 to 92)	57 (−3 to 82)	46 (−44 to 82)
Real-time PCR positive	10 (1.9)	18 (3.5)	15 (7.3)	0.26 (0.11 to 0.63)	0.48 (0.23 to 1.02)	0.55 (0.23 to 1.26)	74 (37 to 89)	52 (−2 to 77)	45 (−26 to 77)
Culture or real-time PCR positive	10 (1.9)	21 (4.0)	16 (7.8)	0.25 (0.10 to 0.58)	0.52 (0.26 to 1.07)	0.47 (0.20 to 1.05)	75 (42 to 90)	48 (−7 to 74)	53 (−5 to 80)
Serologic positive†	6 (1.6)	20 (5.5)	11 (7.5)	0.22 (0.07 to 0.63)	0.72 (0.33 to 1.67)	0.30 (0.10 to 0.77)	78 (37 to 93)	28 (−67 to 67)	70 (23 to 90)
Culture or serologic positive†	10 (2.7)	21 (5.8)	12 (8.2)	0.33 (0.13 to 0.84)	0.70 (0.33 to 1.57)	0.47 (0.20 to 1.04)	67 (16 to 87)	30 (−57 to 67)	53 (−4 to 80)

^*Relative reduction in vaccine efficacy was defined as (1 − relative risk) × 100. CI denotes confidence interval, and PCR polymerase chain reaction.

^†These cases were reported for the per-protocol population, defined as the participants who provided all three annual blood specimens according to the timing specified in the protocol. In this population, 367 participants received the inactivated vaccine, 363 the live attenuated vaccine, and 146 placebo.