The risk was 10 times higher with influenza B, five times higher with influenza A (the most common type during that period), 3.5 times greater for respiratory syncytial virus and almost three times higher for other viruses.
"Rather, since vaccination of adults is only approximately 40% to 60% effective in preventing laboratory-confirmed influenza infection, this study shows that if vaccinated patients have influenza of sufficient severity to warrant testing, their risk of acute myocardial infarction is increased to a level that is similar to that among unvaccinated patients".
Kwong said 31 per cent of the patients who experienced a heart attack had not been vaccinated against seasonal flu, although he cautioned the connection "requires a bit of careful interpretation".
Researchers say influenza infection significantly increases the risk of heart attack, particularly in older persons.
The study "should not be interpreted as evidence of a lack of vaccine effectiveness, because this study was not created to evaluate the effectiveness of influenza vaccines", the researchers said.More news: Smith, founder of British post-punk band The Fall, dies at 60
Of those, 20 patients had a heart attack within a week of getting the disease and six of them ultimately died. There are acute triggers - such as infection, someone who is predisposed - but [they] may not have had that heart attack if they had been infection-free.
According to the HSE's weekly surveillance reports, the week ending on 7 January saw the highest rate of people contracting either one of the flu viruses this year, with the majority of cases being among people aged between 15 - 64, followed by people above the age of 65.
They found the chance of a heart attack was increased six times during the week after flu infection compared to the year before or after.
Researchers zeroed in on the date that lab tests confirmed the flu.
Flu can cause swelling or inflammation in the coronary arteries, which can shake loose plaque and cause blockages, cutting off blood flow.More news: Pennsylvania Supreme Court orders state's congressional map redrawn
Of these, 20 patients were found to have experienced a heart attack within seven days of being diagnosed with the flu.
It comes amid an outbreak of strains known as Aussie flu and Japanese flu.
"I've seen 10 people and I'm only halfway through my week", he said on Wednesday, calling this flu season a "pretty nasty one".
"If someone does have the flu, unfortunately there is no cure, but patients can assist their own recovery through taking plenty of rest and drinking lots of fluids as it is easy to become dehydrated".
The most common sign of a heart attack is chest pain or discomfort.
"Address all of the traditional risk factors you have - obesity, high blood pressure, high cholesterol", he said.More news: [Update] Vice President Pence Confirms US Embassy Move to Jerusalem
"And", he says, "If you are sick, stay home so you don't get other people sick". It's safe, you take it just one time and it has minimal side-effects.
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