"For this particular endpoint we didn't see a difference," Dr. Scott D. Solomon of Brigham and Women's Hospital and Harvard Medical School, in Boston, told Reuters Health by phone. "It may very well be that any formulation of the vaccine is better than nothing at all."
The U.S. Centers for Disease Control and Prevention (CDC) recommends annual flu shots for everyone six months of age and older. People with cardiovascular disease (CVD) are at greater risk of complications from flu and adverse outcomes, Dr. Solomon and his colleagues note in JAMA, and have a weaker humoral immune response to standard-dose influenza vaccine than their CVD-free peers.
To investigate whether high-dose influenza vaccine, approved for adults 65 and older, might be more effective than the standard dose in high-risk CVD patients, the authors conducted a randomized controlled trial comparing the two formulations at 157 sites in the U.S. and Canada across three flu seasons. The study included 5,260 patients who had myocardial infarction (MI) in the past year or were hospitalized for heart failure in the past two years.
The event rate for CV or pulmonary hospitalization and death due to any cause was 45 per 100 patient-years in the high-dose group and 42 per 100 patient-years among those who received the standard dose (hazard ratio, 1.06, P=0.21).
Adverse events included injection-site pain, in 26.5%, myalgia in 17.7% and swelling in 6.1%, and were more frequent with the high-dose formulation. There were two serious adverse events in the high-dose group and four in the standard-dose group.
Previous research found that high-dose trivalent influenza vaccine was more effective than a standard-dose formulation for reducing influenza, hospitalization and cardiopulmonary events in medically stable older adults, while another study found the higher-dose formulation was more effective for reducing hospitalization due to pulmonary causes but not mortality, the authors note.
The current study didn't look at rates of influenza infection or illness, Dr. Solomon noted, and "it's certainly possible that influenza illness itself is reduced by the high dose."
Less than half of high-risk CVD patients get the influenza vaccine annually, Dr. Orly Vardeny of the Minneapolis VA Hospital and the University of Minnesota, who also worked on the study, told Reuters Health by phone.
"Other work from a registry called Get With the Guidelines has shown increased vaccine hesitancy in this population over the last number of years," she added.
People may worry that getting the flu shot causes the flu, due to mild side effects like achiness and fever, Dr. Vardeny noted, and these effects may be particularly troubling if patients aren't told about them in advance.
"Influenza and heart disease are 2 of the most common causes of hospitalizations and deaths globally. The study highlights how common these conditions are and the importance of influenza vaccination for people with underlying conditions, like heart disease," Dr. Manish Patel, team lead of the Influenza Prevention and Control Team in CDC's Influenza Division, told Reuters Health by email. Dr. Patel co-authored an editorial accompanying the study with CDC colleague Dr. Timothy M. Uyeki.
"In this study the high-dose influenza vaccine provided similar benefits as the standard-dose vaccine against severe outcomes, such as all-cause deaths and cardiopulmonary hospitalization in patients with high-risk heart disease," Dr. Patel added. "Thus, influenza vaccination is strongly recommended for these patients."
SOURCE: https://bit.ly/37PDkLK and https://bit.ly/2IrfSMb JAMA, online December 4, 2020.
By Anne Harding
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