People give a lot of reasons for not getting a yearly flu shot. It's inconvenient; they fear vaccines; they don't know where to go; it might hurt.

Those reasons for not getting vaccinated may seem a lot less compelling after hearing about an Australian study that found that a flu shot can reduce the risk of heart attack by 45%.

The study took place at a large hospital in Sydney and compared patients 40 and older who were hospitalized for a heart attack to patients at the hospital's outpatient clinics during the flu seasons of 2008-2010.

The researchers found a protective effect against heart attack (vaccine efficiency or VE) of 45% from taking a flu shot.

Heart attack patients were only half as likely to have had a flu shot that flu season. After adjusting their results for factors such as age and smoking status that are known to increase heart attacks, the researchers found a protective effect against heart attack (vaccine efficiency or VE) of 45% from taking a flu shot.

About 10% of their patients had had an undiagnosed case of the flu that year, suggesting that flu can be missed in hospital patients with other illnesses.

Australia (and the UK) offer free flu vaccines to those 65 and older but those under 65 generally have to pay for flu vaccines out of their own pocket. The researchers think their findings argue for expanding Australian flu vaccine programs to adults 50 years of age.

Extending free vaccination to a lower age group has not been considered cost effective. But because of the high occurrence of heart disease in those 50-64, including many who are not aware they have it, the authors think the idea may prove cost effective when heart attacks are factored into the equation.

In the U.S., whether or not a person qualifies for a free flu shot depends both on their insurance and the locality that they live in.

Many clinics offer free flu shots to all. And the CDC recommendation is that everyone over the age of six months get one every year.

Not everyone is satisfied with the study's conclusions.

One reason is that the study only shows that people who got a flu shot were less likely to get a heart attack, not that the flu shot prevented it. Another is that the study found no link between getting the flu and heart attack, only between getting a flu vaccine and having heart attack. Most explanations of why a flu vaccine might prevent a heart attack hinge on its preventing people from getting the flu.

On the other hand, it's bad science to ignore a study just because you can't explain why its results occurred. And even experts who are questioning the meaning of the study results are not arguing against people getting a yearly flu shot.

According to the CDC, over half the men and nearly two-thirds of the women who die suddenly of coronary heart disease have no previous symptoms. So, proven or not, the fact that a flu shot might lower this risk should be an incentive for people who are in the habit of passing them up to start getting them.

The study was published online ahead of print in the journal, Heart.