A new meta-analysis of six randomised controlled trials has found that seasonal influenza vaccination was associated with a 34% lower risk of major adverse cardiovascular events, and people with a recent acute coronary event had a 45% lower risk.
Cidrap reports that the studies took place from 2000 to 2021 in Toronto, Canada, and included participants who were randomised to receive either a flu vaccine or placebo. The studies included 9,001 patients at an average age of 65.5 years; 52.3% had a previous cardiac event.
The authors found that 3.6% of vaccinated patients developed a major adverse cardiovascular event within 12 months of flu vaccination, compared with 5.4% of those who received placebo or control. This means 56 people would have to be vaccinated to prevent one cardiac event.
All told, 1.7% of vaccine recipients died of cardiovascular causes, compared with 2.5% of placebo or control recipients, for a 26% lower risk (risk reduction, 0.74; 95% confidence interval, 0.42 to 1.30; P = .29).
“The effect sizes reported here for major adverse cardiovascular events and cardiovascular mortality (in patients with and without recent ACS [acute coronary syndrome]) are comparable with – if not greater than – those seen with guideline-recommended mainstays of cardiovascular therapy, such as aspirin, angiotensin-converting enzyme inhibitors, β-blockers, statins, and dual antiplatelet therapy,” the authors concluded.
The study appeared in JAMA Network Open.
Association of Influenza Vaccination With Cardiovascular Risk: A Meta-analysis
Bahar Behrouzi, Deepak Bhatt, Christopher Cannon, et al
Published in JAMA Network Open on 29 April 2022
Question Is seasonal influenza vaccination associated with lower rates of adverse cardiovascular events?
Findings In this meta-analysis of 6 randomised clinical trials including 9001 adults who were randomised to influenza vaccination vs matching placebo or standard care, 3.6% of vaccinated patients developed a major adverse cardiovascular event within 12 months compared with 5.4% of those who received placebo or control, a 1.8% significant difference translating into a number needed to vaccinate of 56 patients to prevent 1 event. Higher-risk patients with recent acute coronary syndrome had 45% reduced risk.
Meaning These results suggest that clinicians and policy makers should continue to counsel high-risk patients on the cardiovascular benefits of seasonal influenza vaccination.
Importance Influenza infection is associated with increased cardiovascular hospitalisation and mortality. Our prior systematic review and meta-analysis hypothesised that influenza vaccination was associated with a lower risk of cardiovascular events.
Objective To evaluate, via an updated meta-analysis, if seasonal influenza vaccination is associated with a lower risk of fatal and nonfatal cardiovascular events and assess whether the newest cardiovascular outcome trial results are consistent with prior findings.
Data Sources A previously published meta-analysis of randomised controlled trials (RCTs) and a large 2021 cardiovascular outcome trial.
Study Selection Studies with RCTs published between 2000 and 2021 that randomised participants to either influenza vaccine or placebo/control. Eligible participants were inpatients and outpatients recruited for international multicentre RCTs and randomised to receive either influenza vaccine or placebo/control.
Data Extraction and Synthesis PRISMA guidelines were followed in the extraction of study details, and risk of bias was assessed using the Cochrane Collaboration tool. Trial quality was evaluated using Cochrane criteria. Data were analysed January 2020 and December 2021.
Main Outcomes and Measures
Random-effects Mantel-Haenszel risk ratios (RRs) and 95% CIs were derived for a composite of major adverse cardiovascular events and cardiovascular mortality within 12 months of follow-up. Where available, analyses were stratified by patients with and without recent acute coronary syndrome (ACS) within 1 year of randomisation.
Six published RCTs comprising a total of 9001 patients were included (mean age, 65.5 years; 42.5% women; 52.3% with a cardiac history). Overall, influenza vaccine was associated with a lower risk of composite cardiovascular events (3.6% vs 5.4%; RR, 0.66; 95% CI, 0.53-0.83; P < .001). A treatment interaction was detected between patients with recent ACS (RR, 0.55; 95% CI, 0.41-0.75) and without recent ACS (RR, 1.00; 95% CI, 0.68-1.47) (P for interaction = .02). For cardiovascular mortality, a treatment interaction was also detected between patients with recent ACS (RR, 0.44; 95% CI, 0.23-0.85) and without recent ACS (RR, 1.45; 95% CI, 0.84-2.50) (P for interaction = .006), while 1.7% of vaccine recipients died of cardiovascular causes compared with 2.5% of placebo or control recipients (RR, 0.74; 95% CI, 0.42-1.30; P = .29).
Conclusions and Relevance
In this study, receipt of influenza vaccination was associated with a 34% lower risk of major adverse cardiovascular events, and individuals with recent ACS had a 45% lower risk. Given influenza poses a threat to population health during the COVID-19 pandemic, it is integral to counsel high-risk patients on the cardiovascular benefits of influenza vaccination.
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