Table 5.

Vaccine effectiveness (VE) of TIV against influenza-related hospitalization by early/late season in patients ≥16 years, ≥16–64 years, and ≥65 years

	Influenza Type	Cases	Controls	Unadjusted		Adjusted
		N	N	VE, %	95% CI	VE, %	95% CI
Age ≥ 16 years (all ages)	Early season
	All strains	265	423	48.6	27.9, 63.3	54.4a	29.7, 70.4
	Influenza B	148	230	41.0	8.4, 62.1	44.8b	0.3, 69.5
	Late season
	All strains	263	412	33.8	6.6, 53.0	29.7c	−5.3, 53.1
	Influenza B	198	304	34.1	2.8, 55.4	33.1d	−5.2, 57.5
Age ≥ 16–64 years (younger adults)	Early season
	All strains	109	131	59.0	27.6, 76.8	65.7e	28.2, 83.6
	Influenza B	55	68	60.1	12.7, 81.8	67.1f	2.7, 88.9
	Late season
	All strains	99	140	−8.5	−95.0, 39.6	−36.1g	−171.2, 31.7
	Influenza B	67	93	−27.7	−175.5, 36.7	−52.3h	−251.6, 34.0
Age ≥ 65 years (older adults)	Early season
	All strains	156	292	41.2	9.8, 61.7	52.5i	8.0, 75.5
	Influenza B	93	162	27.4	−25.9, 58.2	36.3j	−45.1, 72.0
	Late season
	All strains	164	272	48.6	21.3, 66.4	62.4k	29.9, 79.9
	Influenza B	131	211	50.9	21.2, 69.4	69.3l	37.4, 84.9

N number of patients, CI Confidence Interval, TIV trivalent influenza vaccine

Early season defined as admissions prior to the admission date of the median influenza case enrolled; Late season defined as admissions after the date of admission of the median influenza case enrolled

Covariate (p value in model):

^a Influenza vaccination (<0.001), age (0.116), antiviral use before onset of illness (0.821), admission from long term care facility (0.001), obesity (0.017), exposed to children aged <5 years in household (0.536), current or past smoker (0.015), medications before onset of illness (0.325);

^b Influenza vaccination (0.049), age (0.099), antiviral use before onset of illness (0.992), admission from long term care facility (<0.001), obesity (0.020), exposed to children aged <5 years in household (0.447), current or past smoker (0.001), medications before onset of illness (0.515);

^c Influenza vaccination (0.088), age (0.383), antiviral use before onset of illness (0.988), admission from long term care facility (0.960), obesity (0.859), exposed to children aged <5 years in household (0.030), current or past smoker (0.003), medications before onset of illness (0.007);

^d Influenza vaccination (0.082), age (0.150), antiviral use before onset of illness (0.992), admission from long term care facility (0.884), obesity (0.764), exposed to children aged <5 years in household (0.060), current or past smoker (0.002), medications before onset of illness (0.018);

^e Influenza vaccination (0.005), age (0.035), antiviral use before onset of illness (0.998), seniors including patient living in the dwelling (0.129), pregnancy (0.994);

^f Influenza vaccination (0.045), age (0.021), seniors including patient living in the dwelling (0.061), pregnancy (0.995), (no patients used antivirals before onset of illness);

^g Influenza vaccination (0.381), age (0.383), antiviral use before onset of illness (0.992), seniors including patient living in the dwelling (0.046), pregnancy (0.264);

^h Influenza vaccination (0.324), age (0.993), seniors including patient living in the dwelling (0.173), pregnancy (0.188), (no patients used antivirals before onset of illness);

ⁱ Influenza vaccination (0.027), age (0.151), antiviral use before onset of illness (0.991), frailty index prior to admission (0.057), exposed to children aged <5 years in household (0.179), medications before onset of illness (0.051);

^j Influenza vaccination (0.283), age (0.220), antiviral use before onset of illness (0.995), frailty index prior to admission (0.030), exposed to children aged <5 years in household (0.399), medications before onset of illness (0.031);

^k Influenza vaccination (0.002), age (0.992), antiviral use before onset of illness (0.993), frailty index prior to admission (0.076), exposed to children aged <5 years in household (0.107), medications before onset of illness (0.397);

^l Influenza vaccination (0.001), age (0.673), antiviral use before onset of illness (0.993), frailty index prior to admission (0.043), exposed to children aged <5 years in household (0.467), medications before onset of illness (0.339)