It is well known that the flu can be dangerous for older and frail people. However, new research shows that the flu is more dangerous for people with high blood pressure. A large population study among people with high blood pressure shows that flu vaccination is associated with a reduced risk of death. The researchers behind the study think that people with high blood pressure should get a flu shot every year.
It usually starts out like a common cold with a cough, sore throat and runny nose. But then your muscles start to ache, your temperature climbs alarmingly and you both sweat and freeze. Although the flu season is not yet here, some people should still pay special attention to new research showing that flu vaccination may be associated with a reduced risk of death among people with high blood pressure.
“Our study shows that flu vaccination among people who have high blood pressure is associated with an 18% lower risk of death during the flu season. Since this vaccination is both inexpensive and harmless, I think that everyone with high blood pressure should get a flu shot every year,” explains the first author, Daniel Modin, Research Fellow, Department of Cardiology, Herlev and Gentofte University Hospital.
Risk of death 18% lower
Little is currently known about how influenza infection affects people with high blood pressure. However, the Danish research group already showed last year that people with heart failure who get flu shots have a reduced risk of death compared with those who are not vaccinated.
Our theory is that the flu stresses the body, and this can trigger heart attacks and strokes. Since people with high blood pressure have an increased risk of heart attack and stroke, we thought that preventing flu through vaccination might also protect against these diseases. However, this had not been investigated.
The researchers used nationwide health registries to identify 608,452 people 18–100 years old with high blood pressure. The researchers monitored how many of these people died after they got flu shots for nine consecutive influenza seasons from 2007 to 2016. They recorded death from all causes but especially focused on cardiovascular causes of death such as heart attack and stroke.
“Overall, we found that vaccination was associated with an 18% reduced risk of dying from all causes; a 16% reduced risk of dying of cardiovascular causes and a 10% reduced risk of dying from a heart attack or stroke. So flu vaccination was clearly associated with a reduced risk of death from diseases that are associated with high blood pressure.”
Flu creates stress
The researchers cannot confirm why flu is associated with cardiovascular diseases. The flu virus attacking the body triggers a strong immune response that combats the flu virus. However, the immune response also leads to inflammation of the body tissues and blood vessels. The researchers’ theory is that this inflammation may increase the risk of having a heart attack or stroke.
People with high blood pressure have a higher risk of developing atherosclerosis. Atherosclerosis is areas of localized deposition of fat and calcium in the walls of blood vessels, also referred to as plaques. If a plaque becomes unstable and ruptures, it can cause blood clots to form in the blood vessels of the heart and brain. We think that the high levels of inflammation resulting from the flu reduce the stability of plaques and thus increase the risk of cardiovascular diseases.
In the influenza seasons the researchers studied, the vaccination coverage of people with high blood pressure ranged from 26% to 36%, so many people with high blood pressure were not vaccinated.
Our results show that if you have high blood pressure, you could benefit by discussing vaccination with your doctor. Not because flu is inherently dangerous. Since vaccination is safe and inexpensive and protects people from getting the flu and perhaps also from having potentially lethal heart attacks and strokes, I really think that people with high blood pressure should strongly consider getting a flu shot every year.
However, Daniel Modin does not think that people with high blood pressure should be afraid of developing a blood clot if they get the flu.
The overall risk of getting a blood clot from a bout of flu is small. Our results simply indicate that this risk may be reduced further by getting vaccinated.
“The flu vaccine and mortality in hypertension. A Danish nationwide cohort study” was presented at the European Society of Cardiology (ESC) Congress 2019. In 2018, the Novo Nordisk Foundation awarded a grant to Daniel Modin’s supervisor, Tor Biering-Sørensen, Associate Professor, University of Copenhagen for the project Influenza Vaccination in Cardiovascular Disease: a Nationwide Epidemiological Study.