A high-dose, trivalent influenza vaccine was no more effective than the standard-dose quadrivalent vaccine at reducing the risk of death or hospitalization for heart or lung-related causes among high-risk cardiovascular patients, according to findings from the INVESTED trial presented Nov. 17 during AHA 2020.

Researchers randomized 5,260 patients from 157 clinical sites in the U.S. and Canada to either a high-dose trivalent influenza vaccine or a standard-dose, quadrivalent vaccine. All participants had experienced a heart attack or been hospitalized for heart failure within two years and had at least one additional risk factor such as kidney disease, diabetes, stroke, peripheral artery disease, or current use of tobacco. Participants could remain in the study for up to three years, between the 2016 and 2019 flu seasons, and received the same type of vaccine each year they were in the study.

Results found no difference in the rates of mortality or hospitalizations for cardiac or pulmonary causes between vaccine formulations (44.5 per 100 patient years for those who received the high-dose vaccine, vs. 41.9 per 100 patient years for those who received standard-dose).

“There are several possible explanations for our findings,” said Orly Vardeny, PharmD, MS, lead researcher of the study. “It is possible that since all participants received the flu vaccine, both formulations similarly reduced the risk for heart and lung hospitalizations. Another possibility is that since participants were already at a very high risk for hospitalization due to their pre-existing heart conditions, and most of the hospitalizations were not attributable to influenza, the incremental benefit of one vaccine over the other would not have overcome the high underlying risk in this population.” 

She also noted it is possible that the extra influenza strain present in the standard-dose vaccine might have offset the benefit of the higher dose.

Researchers did not collect information on how many participants became sick with the flu, so they do not know if the higher dose of the vaccine reduced overall flu infections more than the standard dose in study participants. Vardeny said future research should examine whether other types of the flu vaccine may be more protective for patients with high-risk conditions or whether the high-dose vaccine is more effective in low-risk cardiovascular patients.

Meanwhile, Vardeny noted that the findings “don’t detract from the extremely strong recommendation that all patients with heart disease get vaccinated for influenza,” particularly this year when COVID-19 numbers continue to rise. “Our study showed that vaccine dose may not be as important as getting vaccinated,” she said.

Clinical Topics: Diabetes and Cardiometabolic Disease, Prevention

Keywords: AHA Annual Scientific Sessions, AHA20, Metabolic Syndrome, Primary Prevention, Influenza, Human

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