Twenty-five years ago a study looked at the rate of heart attacks in the United States, and confirmed what every paramedic and ER doctor already knew; that Acute Myocardial Infarctions (AMIs) run as much 53% higher during the winter months than than during the summer.
While many theories have been offered (holiday stress, cold weather, over-indulgence during the holidays, etc.), a growing number of studies have shown that Influenza - and other acute respiratory infections - can act as triggers for heart attacks and strokes.
A few (of many) previously featured in this blog include:
While the exact mechanisms aren't fully understood, we've also seen a number of studies over the past decade linking receipt of the seasonal flu vaccine to a lower risk of cardiovascular events.
- And in 2022, in The Lancet: Influenza Vaccine to Reduce Adverse Vascular Events in Patients with Heart Failure, we saw a study which found that during flu season, the flu vaccine reduced deaths among heart failure patients by 20%.
Specifically, the authors found that ". . . patients who received the influenza vaccine experienced a remarkable risk reduction of over 20% in cardiovascular death". This particular analysis focused on patients with an existing diagnosis of CVDs (Cardiovascular diseases).
I've only posted the abstract and some excerpts, so follow the link to read the analysis in its entirety. I'll have a bit more after the break.
Influenza vaccination and major cardiovascular risk: a systematic review and meta-analysis of clinical trials studiesFatemeh Omidi, Moein Zangiabadian, Amir Hashem Shahidi Bonjar, Mohammad Javad Nasiri &Tala Sarmastzadeh
Scientific Reports volume 13, Article number: 20235 (2023) Cite this article
Cardiovascular events remain a substantial global health concern, necessitating innovative strategies for prevention. This study aims to assess the potential impact of influenza vaccination on major cardiovascular events. A search of the medical English literature was conducted using PubMed/MEDLINE, EMBASE, and the Cochrane CENTRAL up to 1 August 2023. Meta-analysis and stratified analyses were performed to investigate specific outcomes, including myocardial infarction (MI), cardiovascular death, and stroke. Pooled relative risks (RR) along with their 95% confidence intervals (CI) were calculated to evaluate the associations.A comprehensive analysis was conducted on a total of 9059 patients, with 4529 patients receiving the influenza vaccine and 4530 patients receiving a placebo. Among patients who received the influenza vaccine, a notable reduction in the occurrence of major cardiovascular events was observed, with 517 cases compared to 621 cases in the placebo group (RR 0.70; 95% CI 0.55–0.91). The stratified analysis revealed a decreased risk of MI in vaccinated patients (RR 0.74; 95% CI 0.56–0.97) and a significant reduction in cardiovascular death events (RR 0.67; 95% CI 0.45–0.98).This study provides compelling evidence that influenza vaccination is associated with a decreased risk of major cardiovascular events, particularly myocardial infarction, and cardiovascular death. These findings highlight the potential of influenza vaccination as an adjunctive strategy in cardiovascular disease prevention. Further research and exploration of underlying mechanisms are warranted to elucidate the observed beneficial effects.
The significance of influenza vaccination has long been acknowledged in preventing seasonal flu infections, particularly in high-risk populations1,2,3. There are strong recommendations for influenza vaccination where six months and older people especially adults should be vaccinated against influenza4.
Cardiovascular diseases (CVDs) including hypertensive heart disease, ischemic heart disease, atrial fibrillation cerebrovascular disease like stroke, endocarditis, peripheral vascular disease, and other related cardiovascular diseases are a leading cause of morbidity and mortality worldwide5,6.
Differing viewpoints exist regarding the impact of influenza vaccination on CVDs. While certain observational investigations suggest a favorable correlation between influenza vaccination and the reduction in occurrences of cardiovascular incidents like acute myocardial infarction (MI), contrasting epidemiological studies propose the limited efficacy of influenza vaccines7,8,9,10.
Consequently, a comprehensive and updated study becomes imperative. This updated meta-analysis seeks to assess whether a connection exists between influenza vaccination and a decreased likelihood of experiencing cardiovascular events.(SNIP)
Implications of the findings
The observed interaction between influenza vaccination and reduced cardiovascular mortality among patients with recent CVDs is both clinically and epidemiologically significant. Cardiovascular diseases, including heart attacks and strokes, remain the leading causes of mortality worldwide. The potential of influenza vaccination to yield substantial reductions in cardiovascular mortality in this vulnerable patient group warrants serious attention from healthcare providers, policymakers, and researchers.
Clinical relevance and public health impact
By targeting patients with recent CVDs for influenza vaccination, healthcare providers have a potential opportunity to mitigate the risk of cardiovascular death in a cost-effective and widely available manner. Influenza vaccination programs could be tailored to prioritize this high-risk group, thus potentially reducing the overall burden on healthcare systems and improving patient outcomes.
The evidence from the most recent meta-analysis of RCT data is compelling, revealing a significant interaction between influenza vaccination and the reduction of major cardiovascular events among patients with recent CVDs. This finding underscores the potential benefits of targeting this high-risk group for vaccination.
Further research is warranted to elucidate the precise mechanisms driving this association and to explore the long-term impact of influenza vaccination on cardiovascular outcomes. In the meantime, healthcare providers and policymakers should take heed of these findings and consider prioritizing influenza vaccination for patients with recent CVDs as a feasible and potentially life-saving preventive measure.For most young and healthy individuals the flu is perceived as being an unpleasant, albeit short-term infection, from which most people will fully recover in a matter of a few days.
But over the years we've seen growing evidence suggesting that the flu - and other viral infections - can have a more insidious sequelae (see NIH Preprint: Comparing The Impact Of `Long Flu' to `Long COVID').
In 2012, we looked at a study conducted by the University of British Columbia, that found a linkage between a past history of severe bouts of influenza and the likelihood of developing Parkinson’s disease later in life.
According to their research, a severe bout of influenza doubled a person’s chances of developing the neurological condition (Severe flu increases risk of Parkinson's: UBC research).
In 2017's Nature Comms: Revisiting The Influenza-Parkinson's Link, we looked at hypothesis that suggested that repeated flu infections might increase the risk of developing Parkinson's.
Earlier this year, in Neuron: Virus Exposure and Neurodegenerative Disease Risk Across National Biobanks, a study published in Cell Neuron found statistical linkage between viral illnesses and developing neurodegenerative diseases later in life.
And at an AAIC Meeting in 2020 (see Flu & Pneumonia Shots Appear To Reduce Dementia Risk In Elderly, researchers presented evidence suggesting:
● At least one flu vaccination was associated with a 17% reduction in Alzheimer’s incidence. More frequent flu vaccination was associated with another 13% reduction in Alzheimer’s incidence.
● Vaccination against pneumonia between ages 65 and 75 reduced Alzheimer’s risk by up to 40% depending on individual genes.
There is admittedly much we still don't know about the long-term impacts of various viral infections, or through what mechanisms the flu shot might mitigate some of those risks.
While we have a lot of statistical evidence suggesting correlation, proving causality is notoriously difficult.
Still, there is enough here to suggest that the flu vaccine may have some hidden health benefits beyond its modest ability to prevent seasonal influenza infection. Given the devastating impacts of heart attacks and strokes, even a small reduction in cardiovascular events would be welcome news.