Atlanta, GA—Pharmacists should be aware that increasing uptake of influenza vaccination might be more important than ever this flu season, and the COVID-19 pandemic isn’t the only reason.

A new CDC study, published in the Annals of Internal Medicine, finds that the link between influenza and serious cardiovascular outcomes is stronger than previously suspected. The findings are based on a study of more than 80,000 adult patients hospitalized with flu over eight seasons. CDC researchers determined that sudden, serious heart complications were surprisingly common, occurring in about 12% of patients.

“Previous to our study, there had been suggestions between the link, but our study shows just how common it is,” said lead author Eric Chow, MD, an infectious diseases fellow at University of Washington School of Medicine who led the study while at the CDC.

“There are few respiratory viruses we have a vaccine for,” he said. “Our team motto is ‘Get a flu shot.’” 

Researchers say they suspected influenza was playing an outsized role in acute cardiovascular events during the annual season and decided to take a closer look. They examined acute cardiovascular events and determined risk factors for acute heart failure (aHF) and acute ischemic heart disease (aIHD) in adults with a hospitalization associated with laboratory-confirmed influenza.

The cross-sectional study used information from the U.S. Influenza Hospitalization Surveillance Network during the 2010 to 2011 through 2017 to 2018 influenza seasons. Participants were adults hospitalized with laboratory-confirmed influenza and identified through influenza testing ordered by a practitioner.

With acute cardiovascular events documented using ICD-9 discharge codes, the study also took into account sex, race/ethnicity, tobacco use, chronic conditions, influenza vaccination, influenza antiviral medication, and influenza type or subtype.

Results indicate that, among 80,261 adults, median age 69, with flu who had complete medical record abstractions and available ICD codes, 11.7% had an acute cardiovascular event. Researchers point out that the most common such events (non–mutually exclusive) were aHF (6.2%) and aIHD (5.7%). 

The authors also determined that older age, tobacco use, underlying cardiovascular disease, diabetes, and renal disease were significantly associated with higher risk for aHF and aIHD in adults hospitalized with laboratory-confirmed influenza.

The authors suggest that, in the study, under-detection of cases was likely because influenza testing was based on practitioner orders. In addition, they write, acute cardiovascular events were identified by ICD discharge codes and may be subject to misclassification bias.

“In this population-based study of adults hospitalized with influenza, almost 12% of patients had an acute cardiovascular event,” researchers write. “Clinicians should ensure high rates of influenza vaccination, especially in those with underlying chronic conditions, to protect against acute cardiovascular events associated with influenza.”

Especially concerning to researchers is that 5% of patients hospitalized with the flu had a cardiac complication despite having no documented comorbidities.

Overall, 30% of patients with acute heart complications and flu were admitted to the intensive care unit, and 7% died while in the hospital, according to the report.

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