Table 4. Adjusted odds ratios for hospitalization and death by prior and current influenza immunization status.

	Adjusted a odds ratio (95% CI)
Two year prior immunization history; current immunization	Fall	Pre-Influenza	Influenza	Summer
Hospitalizations b
None; unimmunized	Ref	Ref	Ref	Ref
None; immunized	1.34 (1.00, 1.78)	1.38 (1.10, 1.74)	1.29 (1.12, 1.49)	1.35 (1.14, 1.60)
One; unimmunized	1.66 (1.25, 2.20)	1.29 (1.04, 1.61)	1.24 (1.06, 1.47)	1.29 (1.06, 1.57)
One; immunized	0.73 (0.56, 0.94)	1.1 (0.90, 1.29)	1.10 (0.97, 1.25)	0.99 (0.86, 1.15)
Two; unimmunized	2.34 (1.82, 2.99)	1.41 (1.14, 1.73)	1.21 (1.03, 1.43)	1.01 (0.80, 1.27)
Two; immunized	0.60 (0.48, 0.75)	0.89 (0.76, 1.04)	0.77 (0.69, 0.86)	0.78 (0.68, 0.90)
Deaths (All-cause)
None; unimmunized	n/a	Ref	Ref	Ref
None; immunized	n/a	0.76 (0.65,0.89)	0.94 (0.84, 1.05)	1.07 (0.67, 1.18)
One; unimmunized	n/a	1.73 (1.57,1.92)	1.66 (1.51, 1.82)	1.30 (1.17, 1.45)
One; immunized	n/a	0.68 (0.60,0.76)	0.89 (0.81, 0.96)	1 (0.92, 1.09)
Two; unimmunized	n/a	2.45 (2.21,2.72)	1.78 (1.61, 1.96)	1.35 (1.21, 1.51)
Two; immunized	n/a	0.58 (0.53,0.64)	0.71 (0.66, 0.77)	0.79 (0.73, 0.85)

Note. CI = confidence interval. 2003–04 could not contribute to pre-influenza period for hospitalizations and was excluded from all periods for mortality owing to early start to influenza season that year.

^aAdjusted for age, prior pneumococcal immunization, and medical visits prior year.

^bPneumonia, influenza, or acute respiratory disease listed as most responsible admission diagnosis.