Summary table of case–control studies of the association between influenza vaccination and AMI
| Paper, year | Study location | Study design | Participant age Mean (range)* | Prior AMI in study participants | Vaccination of cases n/N (%) | Vaccination of controls n/N (%) | OR (95% CI) | Adjusted confounders | aOR (95% CI) | Risk of bias score |
|---|---|---|---|---|---|---|---|---|---|---|
| Meyers39 | Kansas City, USA | Hospital-based retrospective study with patient follow-up | Cases: 66±11 Controls: 74±11 | Exclusion criteria not reported | 177/335 (52.8) | 126/199 (63.3) | 0.65 (0.45 to 0.93) | Gender, age, BMI, ever smoked, positive family history, previous heart disease, number of URTI, URTI within 2 weeks before AMI | 0.92 (0.60 to 1.42) | Moderate |
| Heffelfinger et al40 | Seattle, USA | Retrospective HMO database study | Cases: 72.9 Controls: 73.7 | Cases: Prior MI excluded Controls: males hypertensive | 494/750 (65.8) | 1145/1735 (66.0) | 0.99 (0.83 to 1.19)† | Age, gender, history of treated hypertension, index year, pre-existing cardiovascular disease, presence of treated hyperlipidaemia, DM, current smoking and COPD/asthma | 0.98 (0.75 to 1.30) | Moderate |
| Macintyre et al27 | Sydney, Australia | Prospective hospital-based study | Aged ≥40 years | Cases: prior AMI eligible (NNR) Controls: 12-month history of AMI, TIA or stroke excluded | 92/275 (33.5) | 184/284 (64.8) | 0.27 (0.19 to 0.39)† | Age, gender, smoking, high cholesterol | 0.55 (0.35 to 0.85) | Low |
| Naghavi et al36 | Houston, USA | Prospective study based in cardiology outpatient department in a university hospital | Cases: 62.9±11.9 Controls: 64.6±13.5 | Cases/controls: All with prior history of MI | 50/109 (45.8) | 73/109 (67.0) | 0.42 (0.24 to 0.72)† | Current smoking, current hypertension, current hypercholesterolaemia, multivitamin, physical activity (20–30 min 3–4 times/week), history of influenza vaccine in previous years, age ≥60 years | 0.33 (0.13 to 0.82) | Moderate |
| Puig-Barbera et al37 | Valencia Autonomous Region, Spain | Prospective hospital-based study in three health districts | Cases: 75.7 (6.8) Controls: 78.8 (7.6) | Prior MI not an exclusion criteria (NNR) | 114/144 (79.2) | 181/258 (70.2) | 1.61 (1.0 to 2.62)† | Propensity score, at least 3 cardiovascular risk factors | 0.13 (0.03 to 0.65) | Moderate |
| Siriwardena et al38 | UK | Retrospective study of representative GP database | Aged ≥40 years | Cases: prior MI excluded Controls: exclusion not reported | 8472/16 012 (52.9) | 32 081/62 694 (51.2) | 1.07 (1.04 to 1.11)† | Age, gender, smoking, DM, hypertension, previous cardiovascular disease, hyperlipidaemia, family history of AMI | 0.81 (0.77 to 0.85) | Moderate |
| Warren-Gash et al28 | London, England | Prospective hospital-based study; 2009–2010 influenza season | Aged ≥40 years 63.6 (IQR 53.3–72.6) | Cases: prior AMI eligible (14/70) Controls: 1-month history of AMI excluded (5/64 prior AMI) | 30/70 (42.9) | 29/64 (45.3) | 0.91 (0.46 to 1.79)† | Age, gender, month of admission and history of AMI | 0.46 (95% CI 0.19 to 1.12) | Low |
*Unless otherwise reported. †Calculated from included data (not reported in original paper).
AMI, acute myocardial infarction; BMI, body mass index; COPD, chronic obstructive pulmonary disease; DM, diabetes mellitus; HMO, health maintenance organisation; IQR, interquartile range; MI, myocardial infarction; NNR, number not reported; URTI, upper respiratory tract infection; TIA, transient ischaemic attack.