NEW YORK (Reuters Health) – A new study provides more evidence that influenza vaccine reduces major cardiovascular events in patients hospitalized for acute coronary syndrome (ACS). In the study, the number needed to treat to prevent one cardiovascular event was 10 patients.

Annual influenza vaccination is currently recommended as a secondary preventive measure in patients with coronary artery disease. “The findings from this study should encourage the physician to prescribe influenza vaccine to ACS patients,” Dr. Arintaya Phrommintikul from Chiang Mai University in Thailand noted in an e-mail to Reuters Health.

The study involved 439 patients who had been admitted to the hospital due to ACS within eight weeks during November 2007 and October 2008; 221 received inactivated influenza vaccine and the remaining 218 control subjects remained unvaccinated against influenza.

During follow-up lasting up to 12 months, major cardiovascular events (the primary end point) occurred in 21 vaccinated patients compared with 42 in unvaccinated patients (9.5% vs 19.3%), yielding an unadjusted hazard ratio (HR) of 0.70 (P = 0.004). Ten vaccinated patients were hospitalized for ACS compared with 23 unvaccinated patients (4.5% vs 10.6%; unadjusted HR 0.73; P = 0.032).

The beneficial effects of influenza vaccine were consistent across all subgroups and persisted (HR 0.67) after adjustment for variables affecting major cardiovascular events including age, sex, serum creatinine, medication and coronary revascularization.

The secondary outcome, rate of cardiovascular death at 12 months, did not differ significantly between the vaccine group and the control group (2.3% vs 5.5%; unadjusted HR 0.39; P = 0.088).

To put their findings into perspective, the researchers say there have been two randomized controlled studies looking at the effects of the influenza vaccine in patients with coronary artery disease, with mixed results.

The FLUVACS study involved patients with acute myocardial infarction as well as those having planned percutaneous coronary intervention. It demonstrated a significant reduction in cardiovascular mortality and major adverse cardiovascular events. However, in a subgroup analysis the benefit was confined to the group with acute myocardial infarction.

The FLUCAD study, on the other hand, recruited patients with optimally-treated coronary artery disease; only about one quarter of them had ACS. In this study, influenza vaccine had no effects on cardiovascular death, although patients receiving the vaccine had a significantly lower rate of coronary ischaemic events than the control group.

“The study populations were different between the two studies, (which) might contribute to the inconclusive results,” Dr. Phrommintikul noted.

In their study the influenza vaccine clearly reduced major cardiovascular events after hospitalization for ACS and “therefore, it should be encouraged as a secondary prevention in this group of patients,” they conclude.

Reference:

Influenza vaccination reduces cardiovascular events in patients with acute coronary syndrome


Eur Heart J 2011. Published online February 2, 2011.