Vaccinate to Prevent AF? Risk in Seniors Falls After Flu Shot

Pam Harrison

February 08, 2016

TAIPEI, TAIWAN — Getting hit by the flu sometime within the past year, among those not vaccinated against it, raises the risk of developing atrial fibrillation (AF) by a significant 18%, while the risk drops a significant 12% for those who are vaccinated against and don't contract the flu, suggests a large observational study based on 10 years of health insurance records in Taiwan[1]. The analysis also suggested that persons who develop influenza despite having been vaccinated had a risk of developing AF similar to the reference group, those without flu or vaccination.

The findings support the view that "influenza infection may increase the risk of AF, and the risk could be reduced through vaccination," write Dr Ting-Young Chan (Taipei Veterans General Hospital, Taiwan) and colleagues in their report published February 1 in Heart Rhythm. "High-risk patients should be encouraged to receive influenza vaccination annually."

There are reasons to consider the findings merely speculative, observed Dr Charlotte Warren-Gash (Imperial College London, UK) for heartwire from Medscape. Aside from the study's limited observational nature, "we also know that vaccinated people tend to be healthier, and they are generally at lower risk for having problems like AF." Conversely, people who are quite unwell may be a higher risk for AF, yet they may avoid vaccination because they are frail, said Warren-Gash, who was not involved in the study.

And the observed time interval for a history of influenza and development of AF questions the biological plausibility of the conclusions. Most plausible "would be that you would have influenza infection and it would trigger AF within a period of a few days," she noted. "But this study looked at a whole year before patients got AF, and it would not be very plausible that influenza would trigger AF a year later. So it would have been better to do a prospective study where you could see the time interaction between influenza infection and AF."

National Health Insurance Data

The authors identified 11,373 patients with newly diagnosed AF from the National Health Insurance Research Database (NHIRD), a mandatory health insurance program that covers all Taiwanese residents. Controls consisted of four people without AF, matched by age and sex, per case of AF, for a total control cohort of 45,496 patients (mean age 71).

Hazard ratio (HR) for New AF

Group HR 95% CI P
Those contracting influenza without vaccination (n=1369) 1.182 1.014–1.378 0.032
Those vaccinated who did not contract influenza (n=16,452) 0.881 0.836–0.928 <0.001
Those contracting influenza after vaccination (n=696) 1.136 0.929–1.389 0.214

"For patients receiving influenza vaccination and without influenza infection . . . influenza vaccination was consistently associated with a lower risk of AF compared with patients without influenza infection and vaccination . . . in different groups of patients stratified by age, sex and important comorbidities," Chan and colleagues reported.

The authors propose that getting the flu might increase the risk of AF by activating inflammatory responses and increasing sympathetic tone.

Is It Flu Prevention Per Se or a Separate Treatment Effect?

"Influenza vaccination could represent another simple, cost-effective intervention to prevent AF. Although the flu vaccine is already recommended for many patient groups, this study suggests that there are even more potential public-health benefits of the vaccine," write Drs Nishant Verma and Bradley Knight (Northwestern University Feinberg School of Medicine, Chicago, IL) in an accompanying editorial[2].

"In addition, this study opens the door to intriguing research opportunities into whether the treatment rather than the prevention of influenza helps prevent AF. Currently, there is a small body of literature examining the electrophysiologic properties of Tamiflu [oseltamivir, Genentech]. However, the results of this study raise the question of whether the acute treatment of the influenza infection itself with neuraminidase inhibitors or addressing the inflammatory response associated with infection may help prevent secondary episodes of AF."

None of the study authors or editorialists had relevant financial relationships.


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