A new study from researchers at the University of Iowa suggests that the flu vaccine may provide protection against heart attacks in older adults, particularly those over age 80.

Scientists have long recognized that deaths due to influenza and deaths from other non-influenza-related diseases follow a similar seasonal pattern. This has lead researchers to suspect that acute infection caused by influenza may trigger events leading to heart attacks and strokes.

To determine if heart attacks and strokes are associated with influenza activity, the UI researchers built a set of time-series models using inpatient data from a national sample of more than 1,000 hospitals.

Across all models, the researchers found consistent significant associations between heart attacks and influenza activity. The study was published online Jan. 3 in the journal Epidemiology and Infection.

In these models, the research team, led by Eric Foster, Ph.D., visiting assistant professor of biostatistics in the UI College of Public Health, used influenza activity to predict the incidence of heart attack and stroke. The team produced national models as well as models based on four geographical regions and five age groups.

“We found that associations between influenza and heart attack increased with age, were greatest in those more than 80 years old, and were found in all geographical regions,” says Foster. “Our findings, in conjunction with findings in other countries, provide another reason for annual influenza vaccination.”

In addition, the second wave of the H1N1 pandemic in autumn 2009 provided further evidence of the relationship between influenza and heart attack, because both series peaked in the same non-winter month.

The researchers did not find an association between influenza and strokes.

“We were surprised,” says Foster, citing a recent German study that found influenza virus infection to be a risk factor for triggering strokes.

While there are a number of possible reasons for this discrepancy, the researchers write that “there are still many reasons for patients at risk for strokes to undergo annual vaccination against influenza.”

The research team also included Joseph Cavanaugh, Ph.D., Ming Yang, Ph.D., and Fan Tang from the College of Public Health and William Haynes, M.D., Alicia Gerke, M.D., and Philip Polgreen, M.D., from the Carver College of Medicine.

Support for this research was provided in part by a grant from the National Institutes of Health as well as a National Institutes of Health Career Investigator Award.