The Centers for Disease Control and Prevention (CDC) explain, "[T]his flu season continues to be particularly challenging," with "influenza activity [...] still on the rise overall."
Among the heart conditions that put people at increased risk during the flu season is heart failure, in which the heart is either unable to pump enough blood toward the arteries or it cannot fill with enough blood.
Scientists from the Nagoya City University Graduate School of Medical Sciences in Nagoya, Japan, have now conducted an analysis of pre-existing studies related to the connection between the risk of all-cause death among those with heart failure and inoculation against seasonal flu strains.
The recent findings — which will be presented at the American College of Cardiology's 67th Annual Scientific Session, due to be held in Orlando, FL — imply that the risk of all-cause mortality among people with heart failure in the flu season is slashed by half after vaccination against influenza.
"It is well known that influenza infection is associated with increased risk for mortality in heart failure patients. Given the high mortality rate and the relatively low influenza vaccination rates in heart failure patients worldwide, our study supports a wider use of influenza vaccination in heart failure patients."
Lead study author Hidekatsu Fukuta
Reduced risk of hospitalization and death
The researchers conducted an analyisis of six different studies spanning three continents — North America, Europe, and Asia — which together held data on more than 78,000 people with heart failure.
Of these studies, five were observational and looked at associations inferred from patients' health records and one was a retrospective analysis, weighing in on the results of a clinical trial.
Fukuta and team were unable to find any existing randomized control trials testing the direct effects of flu shots on people with heart failure.
The results of the analyzed studies all pointed to a significantly diminished risk of all-cause death among people with this condition if they had received a flu shot. The risk was cut by approximately 50 percent during the flu season and 20 percent for the rest of the year.
Moreover, inoculation against the flu was also linked with a 22 percent decrease in the risk of hospitalization for cardiovascular events.
But the studies also revealed that there were wide discrepancies in the numbers of heart failure patients who opted for a flu shot, with the percentage of vaccine-receivers ranging between 28 and 86 percent in various cohorts.
Fukuta and colleagues suggest that this may be due to the fact that different health guidelines vary widely in the advice they offer to heart failure patients when it comes to the necessity of having regular flu shots.
Following their analysis of these existing studies, the researchers note that all results so far seem to indicate that individuals with heart failure should pre-empt any additional health risks about getting vaccinated.
Nevertheless, the study authors note that most of these studies were observational in nature and therefore cannot readily indicate a causal relationship between flu shots and the decreased risk of death. In order to properly test this relationship, the researchers explain that randomized controlled studies will be necessary.
"Randomized controlled studies should be planned to confirm our observed potential survival benefit of influenza vaccination in these patients," says Fukuta.