A new study suggests the risk of a heart attack could be six times higher when people have the flu. 

In the week after a flu diagnosis, a person could be up to six times more likely to have a heart attack than at any other point during that same year, according to a study presented at the European Congress of Clinical Microbiology & Infectious Diseases. 

The link between flu and heart attacks has been made before, however, previous studies did not include information from death records, meaning out-of-hospital deaths from heart attacks were not included.

A new study used the results of tests from 16 laboratories across The Netherlands (covering around 40 per cent of the population), along with death and hospital records to produce a more complete picture.

A total of 26,221 cases of influenza were confirmed by the laboratories between 2008 and 2019. Of these, 401 individuals had at least one heart attack (myocardial infarction) within one year of their flu diagnosis (419 heart attacks in total).

Of the 419 heart attacks, 25 were in the first seven days after flu diagnosis, 217 within the year before diagnosis and 177 in the year after flu diagnosis (not including the first seven days.)

Around a third of the individuals (139/401) died, of any cause, within a year of being diagnosed with flu.

The researchers calculated that the individuals studied were 6.16 times more likely to have a heart attack in the seven days following a flu diagnosis than in the year before or after. 

The influenza virus is known to increase the coagulation (the “stickiness” or clotting of blood).  It is thought that this, along with the inflammation that is part of the body’s immune response against the virus, can weaken fatty plaques that have built up in the arteries. If a plaque ruptures, a blood clot can form, blocking the blood supply to the heart and causing a heart attack.

Lead author Dr Annemarijn de Boer concludes: “With the potential public health implications of an association between influenza virus infection and acute heart attacks, showing robustness of results in a different study population is important”.

“Our results endorse strategies to prevent influenza infection, including vaccination.  They also advocate for a raised awareness among physicians and hospitalised flu-patients for symptoms of heart attacks.

“While it isn’t clear from our results if those with less severe flu are also at risk, it is prudent for them to be aware of the link.”