Repeated influenza vaccination and hospitalization outcomes among older patients with cardiovascular or respiratory diseases

Figures & data

Table 1. Patients’ characteristics by history of repeated vaccination

	Vaccination history
	None		Current only		Current & previous		Penultimate & previous		All three
Cardiovascular diseases
Periods of observation	77,741		1768		1707		3911		8667
Age (year)	72.8 (8.8)		71.4 (7.9)		73.5 (7.8)		75.6 (6.8)		75.1 (6.5)*
Female, %	43.3		38.3		42.7		42.1		40.4*
Tertiary hospital, %	64.9		64.3		64.9		66.9		65.2
Inpatient visit	3.4 (4.4)		2.5 (2.6)		2.4 (2.5)		3.3 (3.9)		2.4 (2.5) *
CCI	1.6 (1.0)		1.5 (1.0)		1.5 (1.0)		1.6 (1.0)		1.5 (1.0)
Surgical operation, %	30.7		36.1		32.9		30.2		33.7*
Alcohol-related diagnoses, %	0.09		0		0.10		0.10		0.10
Obesity-related diagnoses, %	63.7		68.6		67.6		62.4		65.2*
Respiratory diseases
Periods of observation	44,767		931		823		2635		4579
Age (year)	76.9 (9.1)		74.4 (9.0)		76.1 (8.5)		78.2 (7.1)		77.3 (6.9)
Female, %	45.2		36.7		43.1		36.6		39.1*
Tertiary hospital, %	64.0		69.0		65.4		64.1		64.5
Inpatient visit	4.2 (5.8)		2.7 (2.5)		2.3 (2.2)		4.8 (6.1)		2.6 (2.6) *
CCI	1.6 (1.0)		1.4 (1.0)		1.5 (0.9)		1.5 (0.9)		1.5 (0.9)
Surgical operation, %	15.9		15.4		14.0		15.5		13.9*
Alcohol-related diagnoses, %	0.2		0		0.1		0.1		0.07*
Obesity-related diagnoses, %	30.7		34.3		35.8		31.3		36.2*

Values are mean (SD) for continuous variables or proportions for categorical variables.

Abbreviations: CCI, Charlson Comorbidity Index.

*For all variables, p-values are <0.05 for differences across 5 repeated vaccination categories. An asterisk denotes that p-value is <0.05 for the difference between patients vaccinated in all three seasons and in none of the three seasons.

Table 2. The effectiveness of repeated vaccination among patients hospitalized for cardiovascular diseases

Outcome, metric	Current only	Current & previous	Penultimate & previous	All three
	Effect size (95% CI)	Effect size (95% CI)	Effect size (95% CI)	Effect size (95% CI)
In-hospital death, OR
Influenza seasons	0.76 (0.43, 1.34)	0.62 (0.36, 1.07)	0.79 (0.59, 1.06)	0.48 (0.36, 0.64)
Summer months	0.47 (0.19, 1.15)	0.56 (0.25, 1.27)	0.44 (0.22, 0.91)	0.73 (0.52, 1.01)
Ratio of ORs	1.71 (0.60, 8.32)	1.17 (0.42, 5.64)	1.77 (0.92, 4.96)	0.66 (0.44, 1.03)
Re-admission, OR
Influenza seasons	0.94 (0.62, 1.42)	0.77 (0.44, 1.35)	1.06 (0.85, 1.32)	0.78 (0.61, 1.01)
Summer months	0.92 (0.58, 1.47)	1.17 (0.70, 1.95)	0.87 (0.57, 1.32)	1.09 (0.86, 1.38)
Ratio of ORs	0.99 (0.55, 1.86)	0.65 (0.36, 1.20)	1.23 (0.81, 1.83)	0.71 (0.53, 0.96)
Length of hospital stay, β
Influenza seasons	−1.14 (−1.68, −0.61)	−1.41 (−1.97, −0.85)	−0.43 (−0.95, 0.08)	−1.33 (−1.61, −1.04)
Summer months	−0.66 (−1.26, −0.06)	−0.94 (−1.62, −0.25)	−0.58 (−1.38, 0.23)	−0.80 (−1.16, −0.45)
Difference in βs	−0.47 (−1.23, 0.26)	−0.47 (−1.27, 0.33)	0.13 (−0.61, 0.97)	−0.51 (−0.91, −0.11)
Direct medical costs, GMR
Influenza seasons	0.74 (0.57, 0.96)	0.63 (0.45, 0.88)	1.11 (0.97, 1.27)	0.76 (0.67, 0.88)
Summer months	0.86 (0.60, 1.25)	0.64 (0.43, 0.97)	0.78 (0.56, 1.09)	1.00 (0.82, 1.21)
Ratio of GMRs	0.84 (0.53, 1.32)	0.98 (0.61, 1.59)	1.42 (1.04, 1.94)	0.77 (0.60, 0.95)

The reference group was those not vaccinated in any of the three seasons. The model adjusted for age, age square, sex, number of inpatient visits in the past 12 months, Charlson Comorbidity Index, operation status, hospital size, alcohol-related diagnosis, and obesity-related diagnosis and was stratified by quintiles of propensity score. Effect estimates in influenza seasons were adjusted for unmeasured confounding in summer months. Abbreviations: OR, odds ratio; β, regression coefficient; GMR, geometric means ratio.

Table 3. The effectiveness of repeated vaccination among patients hospitalized for respiratory diseases

Outcome, metric	Current only	Current & previous	Penultimate & previous	All three
	Effect size (95% CI)	Effect size (95% CI)	Effect size (95% CI)	Effect size (95% CI)
In-hospital death, OR
Influenza seasons	0.39 (0.23, 0.66)	0.34 (0.20, 0.60)	0.72 (0.58, 0.89)	0.32 (0.25, 0.41)
Summer months	0.87 (0.51, 1.48)	0.55 (0.27, 1.11)	1.13 (0.81, 1.58)	0.47 (0.34, 0.65)
Ratio of ORs	0.44 (0.20, 0.95)	0.63 (0.24, 2.02)	0.64 (0.44, 0.95)	0.68 (0.46, 0.98)
Re-admission, OR
Influenza seasons	0.68 (0.42, 1.10)	0.35 (0.16, 0.76)	0.99 (0.79, 1.24)	0.95 (0.76, 1.18)
Summer months	0.57 (0.31, 1.05)	0.69 (0.34, 1.42)	0.56 (0.37, 0.85)	0.53 (0.38, 0.74)
Ratio of ORs	1.17 (0.57, 3.73)	0.49 (0.18, 1.43)	1.69 (1.15, 2.59)	1.76 (1.24, 2.51)
Length of hospital stay, β
Influenza seasons	−1.04 (−1.82, −0.26)	−1.44 (−2.19, −0.69)	−1.56 (−2.14, −0.98)	−1.71 (−2.13, −1.28)
Summer months	−0.55 (−1.54, 0.44)	−0.60 (−1.58, 0.38)	−0.36 (−1.33, 0.62)	−1.21 (−1.64, −0.78)
Difference in βs	−0.52 (−1.70, 0.62)	−0.84 (−2.05, 0.39)	−1.23 (−2.15, −0.35)	−0.52 (−1.07, 0.07)
Direct medical costs, GMR
Influenza seasons	0.89 (0.62, 1.28)	0.59 (0.36, 0.98)	0.95 (0.77, 1.16)	0.66 (0.54, 0.82)
Summer months	0.86 (0.52, 1.43)	0.92 (0.49, 1.72)	0.94 (0.62, 1.43)	0.81 (0.61, 1.07)
Ratio of GMRs	1.02 (0.57, 1.84)	0.66 (0.31, 1.48)	1.00 (0.69, 1.50)	0.84 (0.61, 1.13)

The reference group was those not vaccinated in any of the three seasons. The model adjusted for age, age square, sex, number of inpatient visits in the past 12 months, Charlson Comorbidity Index, operation status, hospital size, alcohol-related diagnosis, and obesity-related diagnosis and was stratified by quintiles of propensity score. Effect estimates in influenza seasons were adjusted for unmeasured confounding in summer months. Abbreviations: OR, odds ratio; β, regression coefficient; GMR, geometric means ratio.

Figure 1. The effectiveness of current season vaccination among patients hospitalized for CVDs or respiratory diseases stratified by vaccination history.

The model adjusted for age, age square, sex, number of inpatient visits in the past 12 months, Charlson Comorbidity Index, operation status, hospital size, alcohol-related diagnosis, and obesity-related diagnosis and was stratified by quintiles of propensity score. Effect estimates in influenza seasons were adjusted for unmeasured confounding in summer months. Abbreviations: OR, odds ratio; β, regression coefficient; GMR, geometric means ratio.