Flu Vaccine Protective Against Stroke, CV Events?

July 30, 2020

The rate of seasonal flu vaccination among high-risk groups in the United States, such as those older than 50 years and nursing home residents, is extremely low. However, those who do get a flu vaccination have a significantly lower risk for cardiovascular events, new research suggests.

A large retrospective cohort study showed that participants who received vaccination had a lower risk for transient ischemic attack (TIA), myocardial infarction (MI), and all-cause mortality in the following year versus those who did not receive vaccination.

"Our results highlight the marked underutilization of flu vaccine in high-risk groups and underscores the need for a healthcare policy initiative to increase flu vaccinations among all patients and especially in high-risk groups," study author Roshni A. Mandania, BS, Texas Tech University Health Sciences Center, El Paso, told Medscape Medical News.

"Our hope is to spread awareness and educate as many people as we can about the effectiveness of the flu vaccine and its benefits against serious cardiac complications in all populations, but especially those deemed at high risk," Mandania said.

The data were presented on July 27 at the virtual American Heart Association (AHA) Basic Cardiovascular Sciences 2020 Scientific Sessions.

Low Vaccination Rates

For the study, the researchers analyzed data from the 2014 National Inpatient Sample, the largest database of US hospitals. They also assessed flu vaccination rates during hospitalization in patients designated by the Centers for Disease Control and Prevention as high risk for the flu and its complications.

High-risk patients included adults older than 50 years, those with chronic medical conditions, those with HIV infection, American Indians and Alaskan natives, and those with obesity.

Results showed that of the 7,056,314 total high-risk patients in the database, just 168,325 received a flu vaccination.

Adults over the age of 50 years had a vaccination rate of 1.8% compared with 15.3% in the general population.

But these older adults who were vaccinated had better outcomes in the year following vaccination, with a 28% lower risk of MI, a 73% lower risk of death, a 47% lower risk of TIA, and a 73% lower risk of all-cause mortality.

The vaccination rate for patients with HIV was 2.2% compared with 8.2% who did not have HIV infection. In these individuals, flu vaccination was associated with a 24% reduction in MI, a 23% reduction in TIA, and a 78% reduction in all-cause mortality.

The vaccination rate for nursing home residents was 1.8% compared with 9.5% for those living independently. Flu vaccination in nursing home residents was associated with a 14% reduction in MI and a 56% reduction in TIA.

Among patients with obesity, 2.4% were vaccinated compared with 9% of those with a healthy weight. And flu vaccination in obese patients was associated with a 41% reduction in MI, a 55% reduction in TIA, and a 76% reduction in all-cause mortality.

"Staggering" Results

"The results we found are staggering. It's hard to ignore the positive effect the flu vaccine can have on serious cardiac complications," Mandania said.

"These high-risk groups should have the highest vaccination rates because they are the most at risk. However, our findings show the opposite: flu vaccinations are underutilized," she added.

Mandania noted that some individuals do not view flu vaccinations as necessary or important, while others may face barriers to accessing healthcare including receiving the flu vaccine.

The study assessed immunization solely in hospital, so it is possible some individuals may have received the flu vaccine in an outpatient setting.

On this point, Mandania explained that guidelines recommend all inpatients age 6 months and older discharged from October to March are screened for influenza vaccine status and should be vaccinated prior to discharge from hospital.

"The National Inpatient Sample therefore provides a unique resource for estimating the utilization of flu vaccine in different risk groups. It also provides a comprehensive database with robust documentation to potentially evaluate the effect of flu vaccine on major cardiovascular outcomes including rare outcomes using a big sample size," she said.

"The data are meaningful and provide some insightful findings for developing quality improvement strategies for health care providers and policymakers," she added.

Implications for COVID-19

On the potential mechanism behind the association between flu vaccination and reduced risk of cardiac complications, Mandania suggested that inflammation produced during influenza infection could trigger cardiovascular events.

"Furthermore, lung injury due to the flu can lower blood oxygen levels, which makes the heart work harder. The virus can also directly injure cardiac muscle cells, leading to heart failure," she noted.

Mandania said the need to have the flu vaccine is even more important in the current COVID-19 epidemic. 

"In the same way as flu, COVID-infected individuals with underlying medical conditions are at higher risk for adverse outcomes compared with those at average or low risk. Our research shows that it is a challenge to encourage vaccination in high-risk groups for a disease where prevention may be possible," she said.

"We hope that when a vaccine for COVID-19 is developed, people are more diligent about protecting themselves," she added.

However, as the situation remains critical and with a current lack of a vaccine for the coronavirus, "it is our social responsibility to use the means we have to protect ourselves from what we can — in this case the flu," Mandania said.

"Critically Important"

Commenting on the study for Medscape Medical News, Eduardo Sanchez, MD, AHA's chief medical officer for prevention, said the findings provide additional support for wider use of the flu vaccine, especially in high-risk groups.

The AHA has partnered with the American Lung Association and American Diabetes Association "to collectively deliver a message to providers and to the general public that all adults and all children, by and large, should be getting influenza vaccinations year after year," said Sanchez.

In particular, receiving the annual flu vaccine is "critically important" for patients who have chronic diseases such as high blood pressure, diabetes, or emphysema, he added.

"The potentially serious complications of the flu are far, far greater for those with chronic diseases," Sanchez said.

AHA Basic Cardiovascular Sciences Meeting. July 27, 2020. Presentation 398.

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