A Population-Based Propensity Score-Matched Study to Assess the Impact of Repeated Vaccination on Vaccine Effectiveness for Influenza-Associated Hospitalization Among the Elderly

Figures & data

Table 1 Vaccination Status per Annual Influenza Season Among the Elderly Aged Older Than 65 Years in Taiwan

	2002	2003	2004	2005	2006	2007	2008	2009	2010	2011	2012
Eligible population, no.
Total	63,000	68,634	74,348	80,508	86,860	93,545	100,522	107,438	114,366	121,450	128,511
Vaccination coverage, no.
Not vaccinated	28,454	26,323	34,303	39,594	49,168	57,112	59,820	71,437	84,381	87,851	93,244
Vaccinated	34,546	42,311	40,045	40,914	37,692	36,433	40,702	36,001	29,985	33,599	35,267
Vaccination rate (%)	54.83	61.65	53.86	50.82	43.39	38.95	40.49	33.51	26.22	27.66	27.44
Vaccination status, no.
Not vaccinated	28,454	20,804	20,527	21,069	23,154	25,816	28,056	30,566	34,867	38,396	41,655
First	34,546	13,284	5991	5618	4268	4023	4737	4407	2628	3555	3802
Second		29,027	8119	5365	5807	5223	6229	6327	4222	4956	7078
Third			23,516	5797	3662	3861	3922	3871	3527	2899	3663
Fourth				19,067	4186	2687	3078	2719	2502	2627	2254
Fifth					15,007	3107	2180	2147	1895	1963	2085
Sixth						11,908	2587	1590	1491	1537	1615
Seventh							10,132	1889	1179	1225	1287
Eighth								7693	1406	1005	1034
Ninth									5740	1148	878
Tenth										4689	960
Eleventh											3909
Interrupted		5519	13,776	18,525	26,014	31,296	31,764	40,871	49,514	49,455	51,589
Restarted			2419	5067	4762	5624	7837	5358	5395	7995	6702

Table 2 Demographic Characteristics and Comorbid Medical Disorders for the Trivalent Influenza Vaccine Vaccination and Non-Vaccination Groups Before Propensity Score Matching

		2007			2008
		Vaccinated (36,433)	Non-Vaccinated (57,112)	p-value	Vaccinated (40,702)	Non-Vaccinated (59,820)	p-value
Gender	Male	50.8%	49.6%	0.0003	50.4%	49.6%	0.012
	Female	49.2%	50.4%		49.6%	50.4%
Age (years)	65–74	45.8%	42.2%	<0.001	43.9%	41.6%	<0.001
	75–84	45.7%	42.2%		47.0%	40.5%
	>85	8.5%	15.6%		9.2%	17.9%
Geographic region	North	35.9%	45.4%	<0.001	37.1%	44.7%	<0.001
	Central	29.2%	23.0%		28.7%	23.1%
	South	30.5%	27.3%		29.9%	27.7%
	East	4.4%	4.4%		4.3%	4.5%
Urbanization level	1 (Most urbanized)	19.2%	26.6%	<0.001	20.2%	26.4%	<0.001
	2	23.1%	25.5%		23.5%	25.5%
	3	16.2%	16.7%		16.4%	16.6%
	4	21.7%	17.6%		21.3%	17.7%
	5	5.0%	3.3%		4.7%	3.4%
	6	14.7%	10.3%		14.0%	10.5%
Socioeconomic status	Low	30.7%	38.6%	<0.001	31.2%	38.2%	<0.001
	Moderate	19.5%	20.5%		18.5%	19.8%
	High	49.8%	40.9%		50.3%	42.0%
Number of comorbidities	0	17.3%	24.5%	<0.001	17.2%	24.6%	<0.001
	1–3	69.4%	63.8%		70.2%	64.0%
	>3	13.4%	11.6%		12.6%	11.3%
URI OPD in prior year		1.6	1.1	<0.001	1.5	0.9	<0.001
Number of outpatient visits		29.1	18	<0.001	28.8	16.6	<0.001
Catastrophic illness	Yes	12.4%	19.4%	<0.001	12.4%	21.4%	<0.001
	No	87.6%	80.6%		87.6%	78.7%
Recent intestinal disorder	Yes	14.2%	9.0%	<0.001	12.7%	7.5%	<0.001
	No	85.8%	91.1%		87.3%	92.5%

Abbreviation: URI OPD, outpatient department visit for upper respiratory infection.

Table 3 Demographic Characteristics and Comorbid Medical Disorders for the Trivalent Influenza Vaccine Vaccination and Non-Vaccination Groups After Propensity Score Matching

		2007			2008
		Vaccinated (31,943)	Non-Vaccinated (31,943)	p-value	Vaccinated (33,845)	Non-Vaccinated (33,845)	p-value
Gender	Male	50.5%	49.0%	0.0003	49.8%	48.0%	<0.001
	Female	49.5%	51.0%		50.2%	52.0%
Age (years)	65–74	45.8%	48.0%	<0.001	44.7%	47.8%	<0.001
	75–84	45.1%	44.3%		45.1%	43.9%
	>85	9.1%	7.7%		10.35	8.3%
Geographic region	North	38.1%	39.1%	0.0142	39.2%	40.6%	0.0023
	Central	27.9%	26.9%		27.0%	26.3%
	South	29.6%	29.5%		29.6%	28.9%
	East	4.4%	4.5%		4.3%	4.3%
Urbanization level	1 (Most urbanized)	20.5%	21.4%	0.0012	21.7%	23.0%	<0.001
	2	23.8%	24.3%		24.1%	24.7%
	3	16.6%	16.8%		16.6%	16.8%
	4	21.0%	20.3%		20.3%	19.3%
	5	4.5%	4.4%		4.3%	4.1%
	6	13.6%	12.8%		13.0%	12.2%
Socioeconomic status	Low	32.5%	33.9%	<0.001	33.1%	34.9%	<0.001
	Moderate	19.5%	18.3%		18.2%	17.1%
	High	48.1%	47.8%		48.7%	48.0%
Number of comorbidities	0	18.5%	19.6%	0.0005	18.7%	19.8%	<0.001
	1–3	69.1%	67.5%		69.7%	67.0%
	>3	12.4%	12.8%		11.7%	12.2%
URI OPD in prior year		1.5	1.5	0.4981	1.3	1.4	0.6487
Number of outpatient visits		26.4	26.2	0.1199	25.7	25.2	0.0027
Catastrophic illness	Yes	13.1%	11.5%	<0.001	13.5%	11.6%	<0.001
	No	86.9%	88.5%		86.6%	88.4%
Recent intestinal disorder	Yes	12.9%	12.8%	0.7229	11.4%	11.3%	0.5528
	No	87.1%	87.2%%		88.6%	88.7%

Abbreviation: URI OPD, outpatient department visit for upper respiratory infection.

Table 4 Unadjusted and Adjusted Hazard Ratios of Various Influenza Vaccination Histories Against Influenza-Associated Hospitalization Among the Elderly During 2007–08 and 2008–09 Influenza Seasons

Parameter	2007–08			2008–09
	Unmatched Analysis	Matched Analysis		Unmatched Analysis	Matched Analysis
	Univariate (95% CI)	Univariate (95% CI)	Multivariate (95% CI)	Univariate (95% CI)	Univariate (95% CI)	Multivariate (95% CI)
Current Season Vaccination
No	Ref^a	Ref	Ref	Ref	Ref	Ref
Yes	1.18 (1.10, 1.26)*	0.95 (0.88, 1.03)	1.13 (0.88, 1.47)	1.06 (0.99, 1.13)	0.99 (0.92, 1.08)	1.10 (0.86, 1.41)
Prior Status
Never	Ref	Ref	Ref	Ref	Ref	Ref
First	0.79 (0.68, 0.91)*	1.09 (0.86, 1.39)	1.26 (0.85, 1.88)	0.72 (0.63, 0.83)*	1.16 (0.92, 1.48)	1.21 (0.80, 1.81)
Sequential	0.84 (0.78, 0.92)*	1.04 (0.91, 1.18)	1.19 (0.93, 1.53)	0.74 (0.68, 0.80)*	1.00 (0.88, 1.13)	1.05 (0.80, 1.38)
Interrupted	0.71 (0.65, 0.77)*	1.36 (1.15, 1.60)*	1.10 (0.88, 1.36)	0.74 (0.67, 0.80)*	1.24 (1.06, 1.46)*	0.95 (0.76, 1.18)
Restarted	0.62 (0.53 ,0.73)*	1.55 (1.16 ,2.07)*	1.04 (0.65, 1.68)	0.60 (0.51, 0.69)*	1.51 (1.15 ,1.99)*	1.44 (0.89, 2.33)
Interaction of Current and Prior Vaccination Status
Vac x Never			Ref			Ref
Vac x First			0.76 (0.44, 1.34)			0.82 (0.47, 1.44)
Vac x Sequential			0.60 (0.42, 0.86)*			0.67 (0.46, 0.97)*
Vac x Interrupted			0.96 (0.65, 1.41)			1.09 (0.74, 1.60)
Vac x Restarted			1.07 (0.55, 2.06)			0.70 (0.37, 1.32)
Age Group
68–74 years			0.45 (0.39, 0.53)*			0.45 (0.39, 0.53)*
75–84 years			Ref			Ref
>85 years			2.12 (1.71, 2.62)*			2.55 (2.06, 3.18)*
Gender
Male			Ref			Ref
Female			0.63 (0.55, 0.72)*			0.61 (0.54, 0.71)*

Notes: *p<0.05; ^aRef: reference group.

Abbreviations: CI, confidence interval; Vac, vaccination.

Figure 1 Adjusted vaccine effectiveness (VE) of sequential or never vaccination history among the elderly with or without current-season vaccination during 2007–08 or 2008–09 influenza seasons.

Abbreviation: CI, confidence interval.

Figure 2 Adjusted vaccine effectiveness (VE) of sequential or never vaccination history among the female elderly aged 68–74 years with or without current-season vaccination during 2007–08 or 2008–09 influenza seasons.

Abbreviation: CI, confidence interval.

Figure 3 Adjusted vaccine effectiveness (VE) of sequential or never vaccination history among the female elderly aged 75–84 years with or without current-season vaccination during 2007–08 or 2008–09 influenza seasons.

Abbreviation: CI, confidence interval.