Table 4 Crude and confounder-adjusted estimates of vaccine effectiveness during the influenza season in the included studies

Bond et al. (2012) [17]

0.79 (0.72–0.87)

0.73 (0.67–0.81)

Age, race, sex, time on dialysis, diagnostic mode, diabetes, comorbidities, laboratory parameters

Campitelli et al. (2011) [7]

0.65 (0.51–0.84)^a

0.61 (0.47–0.79)

Demographics, comorbidities, health care utilization, functional status indicators

Groenwold et al. (2009) [19]

0.86 (0.69–1.06)

0.56 (0.45–0.69)

Age, sex, prior healthcare use (GP visits), comorbidities, medication use

Hottes et al. (2011) [20]

0.87 (0.80–0.94)

0.70 (0.64–0.77)

Age, sex, SES, residency, prior influenza/pneumococcal vaccination, medical visits, Elixhauser index

Jackson et al. (2006) [35]

0.56 (0.52–0.61)^b

0.51 (0.47–0.55)

Age, sex, comorbidities, previous pneumonia hospitalization, number of outpatient visits

Liu et al. (2012) [22]

0.40 (0.34–0.47)

0.42 (0.35–0.49)

Age, comorbidities

McGrath et al. (2012) [23]

0.77 (0.76–0.78)^c

0.71 (0.70–0.72)^c

Age, race, sex, cause of ESRD, vintage, adherence, hospital days, mobility aids, comorbidities, oxygen

Örtqvist et al. (2007) [15]

0.50 (−)

0.56 (0.52–0.60)^d

Age and sex, socioeconomic status, marital status, comorbidities

Schembri et al. (2009) [28]

0.70 (0.58–0.86)^e

0.59 (0.57–0.61)

Age, sex, year and serious comorbidities

Tessmer et al. (2011) [30]

0.85 (0.61–1.17)

0.63 (0.45–0.89)

Age, sex, pneumococcal vaccination status, body mass index, nursing home residency, smoking, previous antibiotic therapy, long-term oxygen therapy, number of comorbidities

Villa-Corcoles et al. (2007) [31]

0.77 (0.65–0.89)

0.63 (0.54–0.74)

Age, sex, chronic lung disease, chronic heart disease, diabetes, hypertension, immunocompromised, immunocompromised x age

Wong et al. (2012) [32]

0.72 (0.67–0.77)

0.67 (0.62–0.72)

Demographics, comorbidities, use of health care service, medication use, special medical procedures

Schembri et al. (2009) [28]

0.3 (0.0–7.4)^e

0.63 (0.55–0.77)

Age, sex, year and serious comorbidities

Mangtani et al. (2004) [16]

1.32 (−)

0.88 (0.84–0.92)

Risk, age, repeat prescription status

Johnstone et al. (2012) [33]

0.77 (0.61–0.97)^f

0.65 (0.58–0.74)

Propensity score (body mass index, age, sex, ethnicity, education, vitamin use, smoking history, alcohol use, history of pneumococcal vaccination), history of coronary artery disease, diabetes, hypertension, stroke, admission to nursing home, use of aspirin, ß-blocker, lipid-lowering drug, angiotensin-converting enzyme inhibitor, angiotensin II inhibitor

Foster et al. (1992) [18]

0.78 (−)^g

0.55 (0.36–0.86)

Sex, race, age, information source, hospital type, region, survival, months, duration of recall

Hottes et al. (2011) [20]

1.09 (0.98–1.21)

0.94 (0.82–1.07)

Age, sex, SES, residency, prior influenza/pneumococcal vaccination, medical visits, Elixhauser index

Jackson et al. (2006) [35]

0.82 (0.75–0.89)^b

0.71 (0.65–0.78)

Age, sex, comorbidities, previous pneumonia hospitalization, number of outpatient visits

Jackson et al. (2008) [5]

1.04 (0.88–1.22)^b

0.92 (0.77–1.10)

Age, sex, asthma, smoking, antibiotics, FEV1, oxygen, previous pneumonia, steroids, other drugs

Mangtani et al. (2004) [16]

1.18 (−)^g

0.79 (0.74–0.83)

Risk, age, repeat prescription status

McGrath et al. (2012) [23]

0.90 (0.87–0.92)^c

0.84 (0.82–0.86)^c

Age, race, sex, cause of ESRD, vintage, adherence, hospital days, mobility aids, comorbidities, oxygen

Ohmit et al. (1995) [26]

1.0 (0.82–1.22)^h

0.68 (0.54–0.86)^h

Sex, age, smoking, information source, region, survival, hospital type

Sung et al. (2014) [29]

0.52 (0.41–0.66)

0.45 (0.35–0.57)

Age, gender, comorbidity condition, hypertension, diabetes, dyslipidemia, arrhythmia, anemia, pneumonia, monthly income, level of urbanization, geographic region

McGrath et al. (2012) [23]

0.93 (0.91–0.95)^c

0.88 (0.86–0.89)^c

Age, race, sex, cause of ESRD, vintage, adherence, hospital days, mobility aids, comorbidities, oxygen

Nichol et al. (2008) [24]

0.77 (−)^g

0.70 (0.56–0.89)

Age, sex, high-risk status, smoking, general health, undergraduate status, medical visits, virus match

Nichol et al. (2009) [25]

0.55 (−)^g

0.48 (0.27–0.86)

Sex, smoking, general health, high-risk status, functionality, activity limits, previous vaccination

Jackson et al. (2002) [21]

1.24 (0.84–1.84)^j

1.06 (0.63–1.78)

Age, gender, severe heart failure during hospitalization, smoking status, comorbidities, medication

Liu et al. (2012) [22]

0.85 (0.76–0.94)

0.84 (0.76–0.93)

Age, comorbidities

Omer et al. (2011) [27]

0.56 (0.33–0.96)^k

0.40 (0.24–0.68)^k

Gestational age, maternal age, multiple births, maternal risk factors and comorbidities, labor/delivery complications, birth defects, insurance, smoking, alcohol, race, education, marital status, weight

Omer et al. (2011) [27]

0.73 (0.40–1.33)^k

0.68 (0.32–1.46)^k

Gestational age, maternal age, multiple births, maternal risk factors and comorbidities, labor/delivery complications, birth defects, insurance, smoking, alcohol, race, education, marital status, weight

France et al. (2006) [34]

0.90 (0.80–1.02)^l

0.96 (0.87–1.07)^l

Infant gestational age at birth, infant sex, maternal age, Medicaid coverage, maternal history of prior influenza vaccination, and maternal high-risk status