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Influenza vaccine linked to reduced risk for acute MI
Influenza vaccination may be protective against the risk for acute MI, according to results of a case-control study.
Researchers in Australia studied 559 participants aged at least 40 years who were referred to a hospital for acute MI from 2008 to 2010. The study included 275 inpatients with acute MI and 284 outpatients without MI.
The researchers investigated whether influenza precipitates acute MI. The primary outcome was laboratory evidence of influenza. The secondary outcome was self-reporting of acute respiratory tract infection at baseline.
More than 33% of patients with acute MI reported receiving the influenza vaccine in the year of study recruitment compared with nearly 65% of the control group (OR=3.7; 95% CI, 2.6-5.2). Among those with acute MI, 12.4% had influenza vs. 6.7% of controls (OR=1.97; 95% CI, 1.09-3.54). All cases of influenza were confirmed by laboratory reports; none had been reported at baseline.
After adjustment for risk factors, influenza was not an independent predictor of acute MI. However, the researchers reported that influenza vaccination was significantly protective (OR=0.55; 95% CI, 0.35-0.85); vaccine effectiveness was 45% (95% CI, 15-65), according to the study abstract. For patients aged 40 to 64 years, the estimated vaccine effectiveness for acute MI prevention was 45% (95% CI, –15 to 73). For those aged at least 65 years, the estimated vaccine effectiveness was 33% (95% CI, –20 to 63).
“Recent influenza infection was an unrecognized comorbidity in almost 10% of hospital patients. Influenza did not predict [acute] MI, but vaccination was significantly protective but underused,” the researchers concluded. “… Clinicians should be aware of influenza and infection as an underlying and poorly diagnosed precipitant or comorbidity in hospitalized patients and of the preventive benefit of influenza vaccine for [acute] MI.”
Disclosure: The study was supported by a grant from GlaxoSmithKline. See the full study for a list of the researchers’ relevant financial disclosures.