The study was published on the Web site of the British Medical journal The Lancet Infectious diseases.
“The message here is so strong and so logical that it is difficult for us to ignore it,” said Dr. Ralph Brindisi, vice president of the American College of Cardiology. “If we can convince cardiac patients to get vaccinated against the flu, eventually that could save lives.”
Approximately one-third of patients with heart problems in the United States receive their vaccine regularly.
Doctors have long known that influenza viruses can aggravate pre-existing medical problems, and that cardiac patients are especially vulnerable during pandemics. Influenza viruses cause inflammation in the body, usually in the lungs. But they can also cause inflammation in the heart itself or in the coronary arteries, which could cause dangerous clots to fall out and generate a heart attack.
Once heart patients get sick with the flu, they are also more vulnerable to complications such as pneumonia or other infections.
“We know that influenza vaccine is effective in preventing influenza and therefore theoretically should be effective in preventing influenza complications,” said Andrew Hayward of University College of London, one of the authors of the research.
He said that two of the studies analyzed showed that heart patients who received an injection with the vaccine suffered fewer strokes than those who did not obtain it.
Hayward said that influenza viruses could act merely as factors that trigger heart attacks in patients with cardiovascular problems.
The flu could cause an event that might have happened anyway, he added.
Experts are not sure if the results of the study apply to healthy people with no history of heart problems. But they do say that influenza viruses could trigger heart attacks in people without apparent heart disease, if they have risk factors such as hypertension or overweight.
For patients with heart problems, doctors said the evidence is clear.