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Evidence Summary

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Flu vaccine reduces cardiovascular events

Udell JA, Zawi R, Bhatt DL, et al. Association between influenza vaccination and cardiovascular outcomes in high-risk patients: a meta-analysis. JAMA. 2013;310:1711-20.

Review question

In adults, does flu vaccine reduce cardiovascular events, such as heart attacks or heart failure?

Background

Influenza, or flu, is a common respiratory infection. Having the flu can lead to complications and sometimes death. Older people and those with conditions like heart disease are more likely to have complications if they get the flu.

The flu vaccine can help reduce the chances of getting the flu.

How the review was done

The researchers did a systematic review, searching for published studies up to August 2013. They found 5 randomized controlled trials with 6469 people (average age 67 years). The key features of the studies were:

  • more than 50 adults were involved (about 36% had cardiac disease);
  • flu vaccine was compared with placebo or no vaccine; and
  • the outcome was a combination of major cardiovascular events—that is, any of death or hospitalization for myocardial infarction (heart attack), unstable angina (chest pain), stroke, heart failure, or emergency coronary revascularization.

What the researchers found

The quality of evidence was strong in 4 trials and weak in 1 trial.

Compared with placebo or no vaccine, flu vaccine reduced the rate of cardiovascular events from 4.7% to 2.9%. This means about 2 fewer people out of 100 who received the flu vaccine had a cardiovascular event at up to 1 year.

In people who had an acute coronary syndrome in the past year, flu vaccine reduced the rate of cardiovascular events from 23% to 10%. The means about 13 fewer people out of 100 people who had an acute coronary syndrome in the past year had a cardiovascular event at up to 1 year.

Conclusion

Flu vaccine reduces cardiovascular events such as heart attacks and heart failure for up to 1 year.

Flu vaccine versus placebo or no vaccine to prevent major cardiovascular events*

Groups

Number of trials and people

Rate of events with flu vaccine

Rate of events with placebo or no vaccine

Risk of cardiovascular events at up to 1 year

All people

5 trials (6469 people)

2.9%

4.7%

About 2 fewer people out of 100 had a cardiovascular event

People who had an acute coronary syndrome in the past year

3 trials (789 people)

10%

23%

About 13 fewer people out of 100 had a cardiovascular event

*Cardiovascular events included any of death or hospitalization for myocardial infarction (heart attack), unstable angina (chest pain), stroke, heart failure, or coronary revascularization.




Glossary

Acute coronary syndrome
A condition, such as a heart attack or chest pain, caused by a sudden reduction of blood flow to the heart.
Angina
Chest pain due to reduced blood flow to the heart.
Coronary revascularization
A procedure to restore the blood supply to the heart. Common types are coronary artery bypass graft surgery (or bypass surgery) and percuntaneous coronary intervention (or angioplasty).
Placebo
A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.
Vascular
The body's network of blood vessels. It includes the arteries, veins, and capillaries that carry blood to and from the heart.

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