Doctors need to take concerted action to ensure that people who are at risk of heart disease receive the influenza vaccine every autumn, according to the authors of a new report published in the European Heart Journal.
Their research shows that influenza epidemics are associated with a rise in deaths from heart disease and that flu can actually trigger the heart attacks that result in death.
However, only about 60% of people in the USA who ought to have a flu jab actually have one and this percentage is even smaller in Europe, said Professor Mohammad Madjid, the lead author of the report.
"Our research has shown that influenza epidemics are associated with a rise in coronary deaths. This calls for more intensive efforts to increase the vaccination rate in people at risk of coronary heart disease. This may be especially important in an influenza pandemic when we would expect to see high mortality amongst the elderly and those suffering from heart problems or who have multiple coronary risk factors," he said. "Between 10 and 20% of people catch flu every year, and I have estimated that we can prevent up to 90,000 coronary deaths a year in the USA if every high risk patient received an annual flu vaccination."
Prof Madjid, who is assistant professor of medicine at the University of Texas-Houston, and a senior research scientist at the Texas Heart Institute in Houston, USA, worked with colleagues in the US and in St Petersburg in the Russian Federation to investigate deaths between 1993 and 2000 in St Petersburg that had been shown by autopsy reports to be due to coronary heart disease.
"This was a population where only a small minority were receiving flu vaccines or statin drugs, so this enabled us to see what happened naturally in the absence of these medicines," said Prof Madjid. "Relying on autopsy reports rather than death certificates enabled us to be much more accurate about the cause of death, because doctors often neglect to list flu on a death certificate if their patients have died from a heart attack and, conversely, heart attack symptoms can be missed in patients suffering from flu and pneumonia."
They found that 11,892 people died from acute myocardial infarction (AMI) (47.8% men and 52.2% women), and 23,000 died from chronic ischaemic heart disease (IHD) (40.1% men and 59.9% women). The peaks in deaths from both AMI and IHD coincided with the times when influenza epidemics and acute respiratory disease (ARD), which often accompanies flu, were at their height. They found that the chances of dying from AMI increased by a third in epidemic weeks, compared to non-epidemic weeks, and the chances of dying from IHD increased by a tenth. This was the same for both men and women and in different age groups.
Researchers believe that flu causes an acute and severe inflammation in the body, which, in some patients, can destabilise atherosclerotic plaques in coronary arteries and cause heart attacks.
Prof Madjid said: "Most people develop atherosclerotic lesions in their coronary arteries in early childhood and these lesions grow over time. Inflammation plays a pivotal role in development and growth of these lesions. Most people in Western countries live with different stages of atherosclerosis and many will never show any clinical manifestations of the atherosclerosis. However, in some patients the quiescent, stable atherosclerotic plaques undergo sudden changes, mainly due to exaggerated inflammation, leading to rupture of these vulnerable plaques and subsequent formation of clots resulting in heart attacks.
"This study shows that flu is an important trigger of heart attacks because flu is a severe infection, with high incidence rates and is readily preventable. Therefore, our results give us a new tool for preventing heart attacks.
"My public health message is that flu is an important killer in cardiac patients. If people can recognise that the flu vaccine has specific cardioprotective effects, then high-risk people will be more likely to make sure that they receive the influenza vaccine every year. We know from our other research that one in three people with heart disease do not consider themselves at high risk for heart-related complications from influenza and therefore do not receive the annual flu shots. Currently, people are not practising as we preach, and doctors need to work to change this."
He urged the European Society of Cardiology to follow the lead set in the USA by the American Heart Association and American College of Cardiology and recommend that all at-risk people should be given flu vaccines. "The vaccine may be even more beneficial for those from deprived socio-economic groups or under-developed countries who are not taking all the recommended cardioprotective medications due to their high cost or lack of access to proper medical care. In contrast, the flu vaccine is inexpensive, easy to administer and could save thousands of lives every year."
Prof Madjid , who directs a research lab dedicated to the effect of flu on the cardiovascular system , pointed out that the implications of the research were even more important with a looming flu pandemic when a much higher percentage of the population could be expected to catch the illness.
"In the majority of influenza epidemics (except for the 1918 Spanish flu pandemic) cardiovascular deaths surpassed any other causes of mortality, including pneumonia. During influenza pandemics, heart disease patients may be considered among the priority groups to receive the vaccine or antiviral drugs. Meticulous use of plaque-stabilising agents such as statins, beta-blockers, aspirin and angiotensin-converting enzyme inhibitors should offer additional protection during an influenza outbreak," he said.
Prof Madjid said that a number of new vaccines were being developed against avian flu virus (the most likely cause of the next flu pandemic), "In addition, we are rapidly stockpiling antiviral drugs (such as Tamiflu), so I think we are likely to have the means of preventing or combating the virus, if nature doesn't take us by surprise this year," he concluded.