TORONTO - Adults who have been vaccinated against a common type of bacterial pneumonia appear to have a dramatically lower risk of having a heart attack than those not given the shot in the arm, Canadian researchers have found.
The study of about 5,000 patients at risk for a heart attack raises intriguing questions about the role of infection and inflammation on the cardiovascular system and offers another possible reason for getting vaccinated against pneumococcal pneumonia, the researchers suggest.
"We know that the pneumococcal vaccination can alter one of the complex mechanisms of atherosclerosis, one of the steps in the formation of atherosclerotic plaque," said principal investigator Dr. Danielle Pilon of the University of Sherbrooke. "So we wanted to see if this could be replicated in clinic."
"The hypothesis was that if the vaccination can alter one of the steps in atherosclerosis formation, perhaps it could decrease the risk of heart attack. And this is what we found."
Atherosclerosis is a disease in which plaque - comprising fat, cholesterol, calcium and other substances in the blood - builds up on the insides of the arteries. Over time, plaque hardens and clogs the arteries, which can lead to potentially fatal heart attacks or stroke.
Pilon, a specialist in internal medicine and clinical pharmacology, said vaccination was associated with a more than 50 per cent decrease in the rate of heart attack following inoculation.
"We didn't expect that much really," Pilon said from Sherbrooke, Que. "For our results, the effect of the vaccine was more evident after a year, but probably it could be more after two or three or five years."
However, she cautioned about over-interpreting the results of the research, which compared about 1,000 patients who had suffered a heart attack with about 4,000 patients who had not had a heart attack, but were at high risk for one. Subjects had a mean age of about 60.
"This is a case-controlled study, so we have to be very careful ... it is still an explanatory study and the results are still to be confirmed, for sure," she said.
Commenting on the study, Dr. Douglas Lee said the results suggest there is a strong link between pneumococcal vaccination and protection from heart attacks. But he noted there are caveats with a study of this kind, which took its patient data from hospital and other health records.
"One of them is: Is this association there? Did they detect this association because people who get vaccinated are also more likely to take other preventive measures that would also put them at lower risk for heart attack?" asked Lee, a cardiologist at Toronto's University Health Network.
"For example, are they more likely to exercise, are they more likely to take medications to treat their high blood pressure or high cholesterol and are they less likely to smoke?"
"And those are important things to consider when trying to decide if it's a true association or not."
In a commentary accompanying the paper, published in this week's issue of the Canadian Medical Association Journal, Dr. Mohammad Madjid of the Texas Heart Institute in Houston said it's reasonable to hypothesize that the vaccination may be protective against cardiovascular events by preventing pneumonia.
Previous research has shown that pneumococcal pneumonia and other respiratory infections, including influenza and SARS, have been shown to trigger a heart attack in some patients. "In fact, during almost all influenza epidemics and pandemics (except the 1918 Spanish flu pandemic), about twice as many people die of cardiac causes as die of pneumonia," Madjid writes.
While the findings need to be confirmed by other researchers, Pilot said it suggests that getting the vaccine may offer protection not just from pneumonia but also for the heart.
In Canada, pneumococcal vaccine is recommended for all those aged 65 and older, for children aged two-plus and adults with a variety of conditions, including chronic heart, kidney or lung disease, diabetes, HIV-AIDS, and other diseases that suppress the immune system.
Yet a relatively low proportion of seniors and others for whom the vaccination is recommended have rolled up their sleeves for the inoculation, said Pilon.
"So now if I had a patient in front of me, I would tell him you need to get the vaccine and at least we should vaccinate the people who should receive it," she said. "And in the meantime, we can reproduce the study in a larger cohort (of subjects) and in other designed types of studies and see if the effects are still there."
Madjid said that until such confirmatory studies are available, doctors should comply with guidelines by increasing vaccination rates among patients at high risk of heart attack and stroke, while at the same time treating them with appropriate medications.
