Getting a seasonal flu vaccine might do a lot more than just prevent you from being walloped by the virus this year. It might also protect your heart, according to a new study out of the United Kingdom.
"Flu vaccination could be associated with a reduction in the risk of heart attack," researcher Niroshan Siriwardena of the University of Lincoln, U.K., said in an e-mail interview.
Dr. Siriwardena and his team traced the medical records of thousands of patients between 2001 and 2007 and found that overall, those who had had the vaccine within the previous year were 19 per cent less likely to have their first heart attack than those who did not have the shot. The study appears in the new issue of the Canadian Medical Association Journal.
Researchers have long known that cardiovascular deaths peak during flu season. For instance, in a 2007 study of a group of largely unvaccinated Russians, deaths from heart attacks jumped by 30 per cent in the general population during flu outbreaks.
The new study involved more than 78,000 patients aged 40 years or older from 379 family practices in England and Wales. Of the total, about 16,000 experienced a heart attack for the first time in their lives during the time period.
Those who had a vaccine between September and mid-November had a 21-per-cent reduction in heart attacks, compared to those who had not had vaccines. Later vaccinations resulted in only a 12-per-cent reduction. (The overall reduction over the course of the full season works out to an average reduction of 19 per cent for those who get the shots.)
The general hypothesis many scientists are exploring is that the vaccine, in itself, does not create some sort of immunity. Instead, simply not getting the flu offers protection against heart attacks. It's believed that when a person gets the flu, inflammation can cause any existing plaque on the walls of blood vessels to rupture, sending potentially fatal blood clots into the bloodstream, and to the heart.
Cardiovascular disease accounted for 30 per cent of all deaths in Canada in 2006, according to the Heart and Stroke Foundation of Ontario. Of those deaths, 23 per cent were due to heart attack.
The researchers also looked for connections between the pneumonia vaccine and heart attacks, because there have been similar patterns found with pneumonia patients and higher rates of cardiovascular deaths. Previous research published in the CMAJ found that the pneumonia vaccine could be associated with a 50-per-cent reduction in the rate of acute heart attacks.
But Dr. Siriwardena, a professor of primary and pre-hospital health care, and his colleagues found that preventing pneumonia didn't affect heart-attack risk in the same way. Patients who had had only the pneumonia vaccine did no better than those who had no vaccines. And the combined pneumonia-flu vaccine offered no additional protection compared with the flu shot alone.
"Our study suggests that the association between pneumococcal vaccination and reduction in heart attack disappears when influenza vaccination is taken into account."
So, even though some flu sufferers go on to develop pneumonia, the risk of heart attack appears to stem from the original flu.
Dr. Siriwardena says that while his study focused on people having their first heart attack, other research has shown that people with a history of heart attacks also benefit from flu vaccination in randomized controlled studies.
For those whose doctors recommend the shots - the elderly or those at high risk of disease - it's a good idea to have a shot to prevent the flu itself, as well as chest complications and hospitalization, he says.
"But also because, if the link between influenza vaccination and heart attack is proven, it could prevent those heart attacks which are sometimes triggered by the flu."