Influenza Vaccination and Acute Myocardial Infarction

Results of a recent case-control study have shown that the influenza vaccination may lower one’s chance of suffering acute myocardial infarction (AMI).

There is a considerable amount of indirect epidemiologic evidence demonstrating influenza as a key contributor to all-cause mortality and cardiovascular and respiratory hospitalizations among elderly persons in particular during winter epidemics. Further, rates of AMI and death during the annual influenza season have been shown to be increased and acute infections in general have been shown to be associated with an increased risk of AMI in previous studies.

There is a dearth of direct evidence, however, of the role of viruses and respiratory infections in the precipitation of ischemic events. Researchers therefore sought to investigate whether influenza is a significant and unrecognized precipitant of AMI in patients aged 40 years and older.

The study was conducted in a tertiary referral hospital in Sydney, Australia, during three consecutive winter seasons (2008-2010). Participants of the study were inpatients with AMI (n=275) and outpatients without AMI (n=284), the latter of whom served as the controls. Primary and secondary outcomes were laboratory evidence of influenza and baseline self-reported acute respiratory tract infection, respectively.

Researchers identified evidence of influenza in nearly 10% of the entire study population (12.4% of cases, n=34; 6.7% of controls, n=19); more than half reported being vaccinated in the year of recruitment.Vaccine effectiveness against influenza was 83.6%.Nearly 25% of participants reported a baseline acute respiratory tract infection (ARTI; 31.1% of cases, 18.6% of controls). Researchers noted that baseline ARTI was significantly associated with AMI on univariate analysis, and ARTI was reported in approximately 22% of vaccinated patients and approximately 27% of unvaccinated patients.

In the multivariate analysis, influenza infection was found to no longer be a significant predictor of AMI. Influenza vaccination was, however, significantly protective, with an estimated vaccine effectiveness for the prevention of AMI of 45% in patients aged 40-64 years and 33% in patients aged ≥65 years.

“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,” the authors write. “Our data should inform vaccination policy and cardiologists should be aware of missed opportunities to vaccinate individuals with ischaemic heart disease against influenza.”

This study was supported by a grant from GlaxoSmithKline. Other funding and disclosure information can be found in the study, which is published online in Heart.

-Meredith Edwards White

Reference

CR MacIntyre, Heywood AE, Kovoor P, et al. Ischaemic heart disease, influenza and influenza vaccination: a prospective case control study. Heart. 2013 Aug 21. Available at http://heart.bmj.com/content/early/2013/08/06/heartjnl-2013-304320.short?g=w_heart_ahead_tab. Accessed August 2013.