Got a heart condition? High blood pressure? Beware of the flu

Influenza vaccination in patients with high blood pressure is associated with an 18% reduced risk of death during flu season, according to research presented today at European Society of Cardiology (ESC) Congress 2019 together with the World Congress of Cardiology.

“Given these results, it is my belief that all patients with high blood pressure should have an annual flu vaccination,” said Daniel Modin research associate at the University of Copenhagen, Denmark. “Vaccination is safe, cheap, readily available, and decreases influenza infection. On top of that, our study suggests that it could also protect against fatal heart attacks and strokes, and deaths from other causes.”

The study used Danish nationwide healthcare registers to identify 608,452 patients aged 18 to 100 years with hypertension during nine consecutive influenza seasons (2007 to 2016).

The researchers determined how many patients had received a flu vaccine prior to each season. They then followed patients over each season and tracked how many died.

They recorded death from all causes, death from any cardiovascular cause, and death from heart attack or stroke. Finally, they analyzed the association between receiving a vaccine prior to flu season and the risk of death during flu season. 

After adjusting for patient differences, in a given influenza season, vaccination was associated with an 18% relative reduction in the risk of dying from all causes, a 16% relative reduction in the risk of dying from any cardiovascular cause, and a 10% relative reduction in the risk of dying from heart attack or stroke.

He said: “Heart attacks and strokes are caused by the rupture of atherosclerotic plaques in the arteries leading to the heart or the brain. After a rupture, a blood clot forms and cuts off the blood supply. It is thought that the high levels of acute inflammation induced by influenza infection reduce the stability of plaques and make them more likely to rupture.”

In a study published earlier this year in Open Forum Infectious Diseases, investigators from Warren Alpert Medical School of Brown University, NYU School of Medicine, University of Groningen, and University of Toronto combed through published data on all-cause mortality rates among heart failure patients who received the influenza vaccine and found that flu vaccination was associated with a 31% decreased risk of all-cause mortality in those patients.

The effect was more prominent (51% lower risk) during influenza season. The authors drew from eight studies published since 2000, which included a total of 82,354 patients (average age of 65) with heart failure. They found that patients who had received seasonal flu vaccine had a reduced risk of all-cause mortality (hazard ratio [HR], 0.69; 95% confidence interval [CI], 0.51 to 0.87), especially during flu season (HR, 0.49; 95% CI, 0.30 to 0.69).

A study in Denmark published in Circulation in December 2018 looked at a cohort of 134,048 patients who were aged 18 years or older and diagnosed with heart failure in the period of January 1, 2003, to June 1, 2015.

The research team, composed of investigators from the University of Copenhagen and Harvard Medical School, found that frequent vaccination and vaccination earlier in the year (before the flu season in Denmark – September to October) were associated with larger reductions in the risk of death compared with intermittent and late vaccination.

Why do people with heart disease need the flu vaccine?

Influenza infection has been associated with an increased risk of heart attacks and worsening of chronic cardiovascular conditions.

Previous research has found that people with heart disease are at least six times more likely to have a heart attack after coming down with the flu. Because of the close relationship between heart failure and respiratory illness, with over half of heart failure complications thought to be triggered by respiratory infection, the role of influenza vaccination, which is widely available at low cost, has been described as a potential disease-modifying intervention.

In addition to the inflammatory effects of influenza infection, which have been linked to increases in atherogenesis, the production of pro-inflammatory cytokines during acute infection may directly depress myocardial contractility. Because of these recent evidences, the authors recommend seasonal flu vaccines for eligible heart failure patients.

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