Influenza is a severe infectious disease. According to the Centers for Disease Control and Prevention the H1N1 strain of Influenza infected an estimated one-third of the world’s population in 1918 and caused 50 million worldwide fatalities. 675,000 of these fatalities occurred in the United States. Without a vaccine, individuals were at the mercy of this deadly virus. The only interventions available were reminiscent of what we had at our disposal to protect ourselves at the beginning of 2020 during the COVID-19 pandemic. Although essential, interventions such as frequent handwashing and social distancing only get us so far. During the COVID-19 pandemic, it is easy to lose sight of the ever-looming threat of Influenza. Even nearly a century following the development of an Influenza vaccine, statistics surrounding Influenza are still quite grim. Influenza results in millions of illnesses each year and is a significant cause of absenteeism and lost productivity. Adults with cardiovascular disease are at a much higher risk of developing complications post-infection.
Heart disease is the leading cause of death in the United States and is highly costly. Observational studies and population-based studies have both shown an increase in acute cardiovascular events associated with Influenza infection. Such results would underscore the importance of Influenza vaccination in those with cardiovascular disease. However, quantifying the risk reduction associated with the Influenza vaccine has historically been problematic due to variation among trials. In March 2021, a study was published in the Journal of the American Heart Association reviewing the impact of the Influenza vaccine on mortality and other outcomes in patients with cardiovascular disease. Multiple databases were reviewed through January of 2020, and a meta-analysis and systematic review were carried out on a total of 16 studies involving a total of more than 230,000 patients. Of the 16 studies, 4 were randomized controlled studies, and 12 were observational studies.
Results showed a significant reduction in all-cause mortality, cardiovascular mortality, and major adverse cardiovascular events at a median of 19.5 months of follow-up compared to controls. Despite drawbacks frequently encountered in meta-analyses such as study design and variation in study duration, the overall analysis strongly supports the provision of Influenza vaccination to enhance survival. Despite the inherent risks of Influenza, it is estimated that only 45% of United States adults were immunized against the Influenza virus during the 2018-2019 season. Considering multiple factors such as the seriousness of Influenza and the immense burden of cardiovascular disease in the United States, the results of this analysis strongly support efforts to advance the Influenza vaccine as a vital component of any comprehensive secondary prevention program to prevent adverse cardiovascular outcomes. Providers should discuss the Influenza vaccination with patients and direct education accordingly, especially for those with underlying cardiovascular disease.