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

From: Frequency and impact of confounding by indication and healthy vaccinee bias in observational studies assessing influenza vaccine effectiveness: a systematic review

Outcome by study Crude OR (95 % CI) Adjusted OR (95 % CI) Confounders considered in the adjusted analysis
All-cause mortality
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
Death due to respiratory event
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
Major adverse vascular event (cardiovascular death or nonfatal myocardial infarction or nonfatal stroke)
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
Hospitalization due to influenza and/or pneumonia
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
Hospitalization for acute coronary syndrome
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
Influenza-like illness
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
Cardiac deathi
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
CVD hospitalization
Liu et al. (2012) [22] 0.85 (0.76–0.94) 0.84 (0.76–0.93) Age, comorbidities
Prematurity
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
Small for gestational age
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
Medically attended respiratory illness in infants
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
  1. aadjusted for season and demographics; badjusted for age and sex; cdata were pooled first from 4 seasons; dadjusted point estimates from season 98/99; eunadjusted odds ratios and 95 % CI calculated from death rates for all seasons (1988–2006); fdata were pooled first from 4 seasons; g95 % CI not reported; hdata from season 1990/91 were used; idefined as death due to myocardial infarction, ischemic heart disease, congestive heart failure, hypertensive heart disease, cardiac arrest, and atrial fibrillation; jadjusted for age; kpoint estimates reported here were calculated for local influenza activity and included periods of regional and widespread influenza activity; lmatched by study site and birth week