Toronto—Pharmacists having a difficult time trying to persuade adults to be vaccinated against influenza might be interested in the results of a new study: The report in The New England Journal of Medicine estimates that the risk of heart attack jumps up six-fold within the week after detection of laboratory-confirmed influenza infection.

The study, led by researchers from the Institute for Clinical Evaluative Sciences (ICES) and Public Health Ontario (PHO) in Canada, found a significant association between acute myocardial infarction (AMI) and acute respiratory infections, especially influenza. 

“Our findings are important because an association between influenza and acute myocardial infarction reinforces the importance of vaccination,” said lead author Jeff Kwong, DNP, MS, MPH. That is especially the case for older adults, patients with influenza B infections, as well as those who never had a heart attack before. The risk also was elevated with other respiratory viruses but not as much as with the flu.

“Our findings, combined with previous evidence that influenza vaccination reduces cardiovascular events and mortality, support international guidelines that advocate for influenza immunization in those at high risk of a heart attack,” Kwong pointed out.

For the study, researchers reviewed nearly 20,000 Ontario adult cases of laboratory-confirmed influenza infection from 2009 to 2014, identifying 332 patients who were hospitalized for a heart attack within 1 year of a laboratory-confirmed influenza diagnosis.

Results indicate the incidence ratio of an admission for AMI during the risk interval, compared to the control interval, was 6.05 (95% confidence interval [CI], 3.86 to 9.50). No increased incidence was observed after Day 7, however.

Incidence ratios for AMI within a week were found to be:
• 10.11 after detection of influenza B
•  5.17 with influenza A 
•  3.51 with respiratory syncytial virus 
•  2.77 with other viruses

The study team concluded that the association was significant. “People at risk of heart disease should take precautions to prevent respiratory infections, and especially influenza, through measures including vaccinations and handwashing,” Kwong advised, adding that patients should not delay medical evaluation for heart symptoms, especially within the first week of an acute respiratory infection.
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