#17,110
As any emergency responder will tell you, the incidence of heart attacks and strokes goes up in the winter months. More than twenty-five years ago, a study looked at the rate of heart attacks in the United States, and found that Acute Myocardial Infarctions (AMIs) run as much 53% higher during the winter months than than during the summer.
Seasonal distribution of acute myocardial infarction in the second National Registry of Myocardial Infarction.While cold weather combined with strenuous physical activity (like clearing snow from sidewalks) is often blamed for this spike, even in balmy Southern California, studies have shown a 33% increase in heart attacks over the holidays (see below).
Spencer FA, Goldberg RJ, Becker RC, Gore JM.
When Throughout the Year Is Coronary Death Most Likely to Occur?
A 12-Year Population-Based Analysis of More Than 220 000 Cases
Robert A. Kloner, MD, PhD; W. Kenneth Poole, PhD; Rebecca L. Perritt, MS
Over the past decade we've seen mounting evidence linking ILIs (Influenza-like-illnesses) to an increased risk of heart attack or stroke. A few studies include:
At the same time we've seen studies that suggest flu vaccines reduce the risk having a heart attack or stroke.
To this list we can add a new, large, population-based study from the University of Calgary, published last week in the Lancet, which found that getting the flu vaccine significantly reduces your odds of having a stroke.
I've reproduced the abstract below, but you'll want to follow the link to read it in its entirety.
Jessalyn K Holodinsky, PhD, Charlotte Zerna, PhD, Shaun Malo, MSc, Lawrence W Svenson, PhD *, Prof Michael D Hill, MD, Show footnotes
Open Access Published:November, 2022
Summary
Background
Respiratory infection can be an immediate precursor to stroke and myocardial infarction. Influenza vaccination is associated with reduced risk of myocardial infarction and hospitalisation for cardiac disease, and influenza vaccination is strongly recommended for patients with heart disease. Evidence on whether the same protective association exists for stroke, and whether this potential effect is consistent across age and risk groups, is conflicting. We aimed to assess the risk of stroke after influenza vaccination in adults.Methods
We obtained administrative data from the Alberta Health Care Insurance Plan (which covers all residents of Alberta, Canada) beginning on Sept 30, 2009, or May 15 of the year in which residents were recorded as being 18 years of age. Individuals were censored at the earliest of three events: death, recorded outmigration, or Dec 31, 2018. The outcome of interest was any stroke event, comprising acute ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, and transient ischaemic attack. We used Andersen-Gill Cox models to analyse the hazard of any stroke event for individuals with recent (<182 days) influenza vaccination compared with those without recent influenza vaccination, with adjustment for age, sex, anticoagulant use, atrial fibrillation, chronic obstructive pulmonary disease, diabetes, hypertension, income quintile, and rural or urban home location. Two-way interaction terms between each individual covariate and vaccination status were used to assess for effect modification by risk factor. The association between vaccination and risk of each type of stroke was also modelled, adjusting for baseline covariates.
FindingsThe study sample consisted of 4 141 209 adults (29 687 899 person-years of observation time) registered under the provincial health-care system between Sept 30, 2009, and Dec 31, 2018. 1 769 565 (42·73%) individuals received at least one vaccination during the study period, and 38 126 stroke events were recorded. Adjusted for demographics and comorbidities, recent influenza vaccination significantly reduced the hazard of stroke (hazard ratio 0·775 [95% CI 0·757–0·793]). This association persisted across all stroke types. We found effect modification by each covariate examined except for home location; however, vaccination was associated with a reduced risk of stroke overall across all ages and risk profiles with the exception of individuals without hypertension.InterpretationThe risk of stroke is reduced among people who have recently been vaccinated against influenza compared with those who have not. This association extended to the entire adult population and was not limited to individuals with a baseline high risk of stroke. Further studies in a variety of settings are needed to evaluate whether influenza vaccination could be used as a public health strategy to prevent stroke.
You'll find an accompanying press release from the University of Calgary at:
Flu vaccine lowers risk of strokeWhile the current flu vaccine is nowhere near as effective as we'd like it to be, and the promise of a universal flu vaccine remains elusive (see J.I.D.: NIAID's Strategic Plan To Develop A Universal Flu Vaccine), there is evidence to suggest the benefits of vaccination may extend beyond preventing influenza infection.
UCalgary study shows a new benefit to the annual influenza shot
