Flu Vaccination and Heart Attacks

Research suggests that doctors should ensure that patients with ischaemic heart disease or at risk for AMI are vaccinated.

Research published by an Australian team of experts led by UNSW Professor Raina MacIntyre, in the journal Heart this week suggests that the flu shot seems to almost halve the risk of heart attacks in middle-aged people with narrowed arteries. Those aged 50 to 64 are not currently routinely included in national flu vaccination programs in either the UK or Australia. The recent findings prompt the Australian authors to suggest that further exploration of extending the schedule may be warranted.

The experts wanted to find out if flu is an unrecognized, but clinically important, contributing factor to increased heart attack risk.  Prior evidence suggests that flu increases the risk of death from all causes as well as the risk of admission to hospital for cardiovascular and respiratory problems.

They therefore assessed 559 patients over the age of 40 who were referred to a tertiary hospital during consecutive winters in 2008-10. Some 275 of these patients had sustained a heart attack; 284 had not. Nose and throat swabs and blood samples taken at admission and 4-6 weeks later showed that around one in eight (12.4%; 34) of the heart attack patients had recently had flu, compared with just under 7% (18) in the comparison group. Half of all the patients had had the flu jab that year.

Flu had not been diagnosed in around one in 10 of all the patients who had the infection, indicating that it may be missed in hospital patients with other clinical problems, say the authors. A recent respiratory infection was more common among those patients who had had a heart attack and doubled the risk. After taking other influential factors into account, such as age, high cholesterol, and smoking, flu did not increase heart attack risk. But vaccination against the infection did seem to be protective, decreasing the risk of a heart attack by 45%. Previous research indicates that infections such as flu might encourage blood to thicken or prompt an inflammatory response in arteries that are already diseased, so sparking the development of a blockage.

Professor Raina MacIntyre, a member of the ISG and Professor of Infectious Diseases Epidemiology at UNSW said:  “Extending the flu vaccination program to 50 to 64 year olds has been a policy debate in the past, but not considered to be cost effective. However, prevention of cardiovascular disease, which is the leading cause of death globally and in Australia, and causes a great deal of illness and death in older adults, wasn’t taken into consideration in such estimates. Our study adds to a considerable weight of evidence that points to influenza vaccine being protective against heart attacks. Given the huge burden of coronary artery disease in society, even a small effect of influenza vaccination in preventing [heart attacks] may have a significant population health impact.” 

Associate Professor Pramesh Kovoor, Head of Cardiology at Westmead Hospital and a co-author said: “Cardiologists should be aware of influenza as an undiagnosed potential precipitation of AMI. We found that 10% of AMI patients have influenza, which has not been picked up during the hospital admission. They should also offer flu vaccine to AMI patients before discharge.”

The authors call for the issues to be explored further, and at the very least say that doctors should be aware that flu is an underlying and poorly diagnosed condition in hospital patients and that the flu jab seems to lessen the risk of heart attack in patients at risk of it. Even if we didn’t vaccinate everyone aged >50 years, influenza vaccination of people with a first heart attack could also have a significant impact, with high rates of subsequent acute coronary events in such patients. Doctors should consider vaccination of heart attack patients before hospital discharge.

To download original article, click here: Ischaemic heart disease, influenza and influenza vaccination: a prospective case control study

Published:  August 2013

Last revised: 17 November 2015