Heart doi:10.1136/heartjnl-2013-304320
  • Epidemiology
  • Original article

Ischaemic heart disease, influenza and influenza vaccination: a prospective case control study

Open Access
  1. Dominic E Dwyer3,6
  1. 1School of Public Health and Community Medicine, UNSW Medicine, the University of New South Wales, Sydney, New South Wales, Australia
  2. 2National Centre for Immunisation Research and Surveillance (NCIRS), The Children's Hospital at Westmead, Westmead, New South Wales, Australia
  3. 3Westmead Hospital, Sydney Medical School, University of Sydney, Westmead, New South Wales, Australia
  4. 4Massachusetts General Hospital, Boston, Massachusetts, USA
  5. 5Faculty of Medicine, University of New South Wales, Sydney, New South Wales, Australia
  6. 6Centre for Infectious Diseases and Microbiology Laboratory Services, Institute of Clinical Pathology and Microbiology (ICPMR), Westmead Hospital, Sydney, New South Wales, Australia
  1. Correspondence to Dr Anita E Heywood, School of Public Health and Community Medicine, UNSW Medicine, The University of New South Wales, Level 2, Samuels Building, Sydney, NSW 2052, Australia; a.heywood{at}
  • Received 20 May 2013
  • Revised 15 July 2013
  • Accepted 19 July 2013
  • Published Online First 21 August 2013


Background Abundant, indirect epidemiological evidence indicates that influenza contributes to all-cause mortality and cardiovascular hospitalisations with studies showing increases in acute myocardial infarction (AMI) and death during the influenza season.

Objective To investigate whether influenza is a significant and unrecognised underlying precipitant of AMI.

Design Case-control study.

Setting Tertiary referral hospital in Sydney, Australia, during 2008 to 2010.

Patients Cases were inpatients with AMI and controls were outpatients without AMI at a hospital in Sydney, Australia.

Main outcome measures Primary outcome was laboratory evidence of influenza. Secondary outcome was baseline self-reported acute respiratory tract infection.

Results Of 559 participants, 34/275 (12.4%) cases and 19/284 (6.7%) controls had influenza (OR 1.97, 95% CI 1.09 to 3.54); half were vaccinated. None were recognised as having influenza during their clinical encounter. After adjustment, influenza infection was no longer a significant predictor of recent AMI. However, influenza vaccination was significantly protective (OR 0.55, 95% CI 0.35 to 0.85), with a vaccine effectiveness of 45% (95% CI 15% to 65%).

Conclusions Recent influenza infection was an unrecognised comorbidity in almost 10% of hospital patients. Influenza did not predict AMI, but vaccination was significantly protective but underused. The potential population health impact of influenza vaccination, particularly in the age group 50–64 years, who are at risk for AMI but not targeted for vaccination, should be further explored. Our data should inform vaccination policy and cardiologists should be aware of missed opportunities to vaccinate individuals with ischaemic heart disease against influenza.

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