Large groups of patients with cardiovascular disease can benefit from this study by Dr. Warren-Gash from the CDC:
Charlotte Warren-Gash C, Smeeth L, Hayward AC. Influenza as a trigger for acute myocardial infarction or death from cardiovascular disease: A systematic review. Lancet Infect Dis 2009.
The study reported that patients with cardiovascular disease has increased likelihood of suffering a sudden coronary event with influenza. Seasonal patterns of influenza also coincides with seasonal patterns of myocardial infarction. It has been hypothesized that influenza can act as an inflammatory stimulus that can act to dislodge atherosclerotic plaques and cause arterial occlusion.
Two small randomized clinical trials assessed protection by flu vaccine against myocardial infarction. Flu Vaccination Acute Coronary Syndromes (FLUVACS) trial showed reduced risk of death from cardiovascular causes. However the effect diminishes with time. FLU Vaccination in Secondary Prevention From Coronary Ischemic Events in Coronary Artery Disease (FLUCAD) trial showed a significant protective effect against coronary ischemic events however there was no significant effect on cardiovascular deaths.
The study is a meta-analysis of various studies dealing with the association with Influenza and cardiovascular events. None of the studies reviewed dealt with the H1N1 strain.