Flu Vaccination Tied to Less MI in Hospitalized Patients

Adults who receive influenza vaccination in the hospital are less likely to have MI, according to a cross-sectional study that adds to accumulating data on the cardiovascular health benefits of protecting patients from the flu.

In an analysis of roughly 30 million US inpatients, the prevalence of MI was 3.4% among those who received flu vaccine in the hospital and 4.4% among those who did not, Mariam Khandaker, MD (Icahn School of Medicine at Mount Sinai St. Luke’s and Mount Sinai West, New York, NY), said in a web briefing with reporters.

After adjustment for potential confounders, in-hospital vaccination was associated with a relative 9% lower risk of MI (RR 0.91; 95% CI 0.87-0.96).

“Given the benefits of flu vaccine, I feel it should be considered as an integral part of CVD management and prevention,” said Khandaker, who is scheduled to present the findings later this week at the American College of Cardiology 2019 Scientific Session in New Orleans, LA.

“Flu vaccination is a very low-cost, yet underutilized, preventive measure for heart attacks,” she added. “It is important for physicians to educate patients about the benefits of vaccination in order to help them make informed decisions.”

Given the benefits of flu vaccine, I feel it should be considered as an integral part of CVD management and prevention. Mariam Khandaker

Khandaker explained that influenza infection stresses the heart by increasing heart rate, which in turn increases oxygen consumption, and by triggering the release of inflammatory cytokines, which can lead to disruption of coronary plaques, thrombogenesis, and blockage of the coronary arteries. One would expect that flu vaccination would reduce these stressors, she said, and indeed, prior studies have suggested that protected patients have fewer MIs.

The current study—one of the largest to examine the relationship between flu vaccination and MI, Khandaker said—was a retrospective analysis of roughly 30 million adults included in the US National Inpatient Sample database for 2014, the most recent year available. The researchers divided the patients into two groups based on whether they received flu vaccine in the hospital that year; about 2% of patients were vaccinated.

The difference in the prevalence of MI observed between vaccinated and unvaccinated patients “corresponded to about 5,000 fewer cases of heart attacks among vaccinated patients than would have been expected otherwise,” Khandaker said. The difference in MI prevalence based on in-hospital receipt of flu vaccine was consistent across patients with NSTEMI, STEMI, and unstable angina.

Salim Virani, MD, PhD (Baylor College of Medicine and Michael E. DeBakey VA Medical Center, Houston, TX), who moderated the briefing, said the study is “building on prior work that flu vaccination just does not reduce the risk of fatal respiratory infections, but may also have a role when it comes to cardiovascular event risk reduction.”

Commenting for TCTMD, Mohammad Madjid, MD (McGovern Medical School at UTHealth, Houston, TX), expressed some concerns about the study, including the fact that it assessed the exposure (flu vaccination) and the outcome (MI) concurrently, which does not allow for a temporal or causal relationship to be established. In addition, he said, there’s no information on whether patients received flu vaccine before the hospitalization, muddying the results.

“With this picture in mind, a cross-sectional study is not the best way to look at this and actually can be misleading,” Madjid said.

The problems with this study, however, should not take away from the larger message about the importance of influenza vaccination, he added, pointing out that there is a growing body of evidence supporting the cardioprotective effects of flu vaccine.

In fact, he said, a science advisory from the American Heart Association and the American College of Cardiology released in 2006 that recommended influenza vaccination for patients with coronary disease or other atherosclerotic vascular conditions should probably be updated to include stronger recommendations based on accumulating supportive data.

“These studies are very good to reinforce our knowledge about this, and this is the time to move forward and improve our prevention in this area, which is still suboptimal,” Madjid said, noting that only 60% to 65% of patients with heart disease receive their flu shot. The goal is to get that figure above 90%, he said, “so there is a big gap and we haven’t been doing a very good job of offering the evidence-based medicine to more patients.”

Citing studies showing links between influenza and other cardiovascular disorders like heart failure and arrhythmias, Madjid concluded by saying: “We know that flu is bad for the heart and we have to prevent it. That’s the simple message to the public and to doctors.”