–Studies find fewer hospitalizations and less dementia after vaccination
Two new observational studies offer new evidence that heart failure patients may benefit from the flu vaccine. The studies were presented in Florence, Italy, at the Heart Failure 2016 and the 3rd World Congress on Acute Heart Failure.
In the first study Kazem Rahimi (University of Oxford) analyzed electronic health records of nearly 60,000 patients with heart failure between 1990 and 2013. He compared outcomes in the year following a vaccination with outcomes in adjacent years with no vaccination. He reported that the flu vaccination was associated with a 30% reduction in the risk of hospitalization due to cardiovascular disease and a 16% reduction in the risk of hospitalization due to respiratory disease.
The association was strongest in the first few months after vaccination and in patients who were 65 years of age or younger. As anticipated, as a validation of the findings, there was no association between vaccination and hospitalization for cancer.
Rahimi noted in a press release that “even in more recent years, only about half of HF patients in our setting received annual influenza vaccination.” He said that higher adoption of the flu vaccine “may help alleviate the burden of influenza-related admissions” in heart failure patients. The lower use of flu vaccines in heart failure patients “may partly be because there is no strong evidence to support the recommendation in these patients.”
“These findings do not suggest that influenza infection causes myocardial infarction or other cardiovascular events,” he said. “A more likely explanation for the reduction in risk of cardiovascular hospitalization is that vaccination reduces the likelihood of an infection which could in turn trigger cardiovascular deterioration.”
Rahimi cautioned that “despite the measures taken, we cannot entirely rule out the possibility of residual confounding explaining at least part of the observed association. But the findings do provide further evidence that there are likely worthwhile benefits and on that basis more efforts are needed to ensure that heart failure patients receive an annual flu jab.”
Can the flu vaccine help prevent dementia?
A second study presented in Florence raised the novel possibility that the flu vaccine might lower the risk of heart failure patients developing dementia. Dr. JC Liu and colleagues in Taiwan analyzed data from more than 20,000 heart failure patients between 2001 and 2012. After adjusting for possible confounding factors they found that the risk of dementia was lower by 35% in patients who received a flu vaccine (HR 0.65, CI 0.60-0.71, [<0.001). The effect was strongest in older patients and in men. Elderly patients who had three or more vaccinations had a 55% reduction in dementia risk.
“Previous studies have shown that there is a link between impairment in cognitive function and heart failure,” said Dr Liu in a press release. “Some reports have also suggested that inflammation after getting the flu might contribute to dementia. However, there are no solid data to demonstrate that influenza vaccination could decrease the relative risk of dementia in patients with heart failure.”
Jacob Udell, (University of Toronto), who has performed earlier research suggesting the cardiovascular benefits of the flu vaccine, said that “these are interesting abstracts and I look forward to seeing both papers published after peer review. The analysis by Rahimi et al, using the self-controlled case series design where each patient acts as their own control during seasons when they skipped a flu vaccine, is a good approach with observational data to minimize (to the extent possible) confounders. I will want to better understand which types of cardiovascular events were lower with flu vaccination and whether the effect was consistent across different etiologies of heart failure. Nevertheless these types of observational studies are another encouraging reason for patients with heart failure to go out and get a vaccine every year. Use of annual flu vaccine in patients with HF is woefully low as data from Dr. Vardeny’s paper suggests when we looked at baseline use around the world within the PARADIGM-HF trial. To definitively determine whether effective flu vaccination reduces the risk of death or cardiopulmonary hospitalization in patients with recent MI or HF, we are planning an NIH funded trial called INVESTED. More details will be coming in the fall.”