The Upshot Series #9

On world heart day, it's time for a flu shot

Published on: September 29, 2021


Scientists have confirmed the unexpected link: influenza can significantly increase the risk of having a heart attack.1 An annual influenza vaccine can reduce that risk by up to nearly half, as much as other prevention measures for cardiovascular disease such as giving up smoking and taking cholesterol-lowering medications.2

“Most people know there are spikes in respiratory diseases like influenza in the winter months, but there are also spikes in the numbers of heart attacks and strokes,” said Bogdana Coudsy, Global Medical Head for Influenza and COVID-19 at Sanofi Pasteur. 

Through rigorous scientific analysis, researchers were able to demonstrate that it’s not simply the cold weather triggering those cardiovascular events, but rather influenza and other infections
Bogdana Coudsy

Bogdana Coudsy

Global Medical Head for Influenza and COVID-19 at Sanofi Pasteur

The flu can trigger a heart attack, vaccination can reduce the risk

The risk for all adults of having a heart attack in the week following an influenza infection is more than 10 times higher than at any other time. There is also an 8-fold increase for strokes during the same week.3,4 Influenza creates inflammation in the body, in the lungs and in the linings of blood vessels and other vital organs.5 For this reason, the infection can cause other severe complications like pneumonia, cardiovascular events or diabetic crises. The oldest and frailest of the population can also suffer irreversible loss of general health, a phenomenon called “functional decline”.6

Influenza vaccination can reduce the risk of heart attack by 15% to 45%, which is similar to the reductions estimated with high-cholesterol medications (19%-30%) or cutting out smoking (32%-43%).2

Dr. Tor Biering-Sørensen, MD, PhD, MPH, and Associate Professor in Health and Medical Sciences at the University of Copenhagen summed it up, “We know today that influenza can cause cardiovascular complications, and an influenza vaccine can reduce the risk of these complications.”1,2

The impact of COVID-19 on flu

In a normal year, before the pandemic, between ~ 50% and ~ 80% of adult populations in OECD countries got their annual flu shot each year.7 Public health recommendations range by geography: in the US anyone can get the annual jab, and Europe prioritizes at-risk populations such as people with underlying conditions and most people in their 60s (and older).

Influenza vaccination has gone a long way already in terms of reducing hospitalizations due to the flu and its complications, and that’s been incredibly important as COVID-19 emerged.  But we can and need to do more.

“We saw a strange epidemiological year in 2020-2021 where very little flu circulated, likely due to social distancing and mask wearing, and travel bans, all in anticipation of that first pandemic winter,” Bogdana said. 

The coming flu season remains unpredictable, with the question remaining-will there be a flu rebound? The situation is unique, and epidemiologists cannot predict with certainty what will happen.8

In the Northern Hemisphere, the influenza season ahead overlaps with the easing of many COVID-19 social restrictions and the back-to-school season, which could result in an increase in transmission of infection. Added to that, experts fear a lower level of population immunity against influenza due to last year’s lockdowns and social distancing rules. The result could be an active flu season with more severe cases and a risk of increased burden on healthcare systems. 

Added Dr. Biering-Sørensen, “In my view, it’s of the utmost importance to increase the vaccine uptake to reduce the burden of cardiovascular complications caused by influenza epidemics.” 

“Most people who get their flu shot will be able to avoid going to the hospital with influenza or an influenza-triggered heart attack this winter,” concluded Bogdana. “Now we need to maximize the number of people in that scenario. It’s such an easy, proven, and cost-effective intervention to just get a vaccine, we need to make sure people are aware of the full extent of its benefits.”

In the context of the COVID-19 pandemic, the US CDC and several additional national health authorities in Europe have recommended co-administration of influenza and COVID-19 vaccines this fall to facilitate broad and timely vaccination against both infections.9,10

Sanofi offers several different kinds of influenza vaccines, which are broadly distributed and administered worldwide. Our standard-of-care quadrivalent vaccines help protect against all four main virus strain types that circulate each flu season and our high-dose vaccines are tailored for adults aged 65 and older. 

As unpredictable and potentially deadly infectious diseases like COVID-19 and influenza continue to evolve, our Sanofi scientists and medical experts continue to pursue better understanding of their transmission and harm to continually develop new vaccines to help prevent and control their impact. 


Explore more

A Look Inside Influenza Vaccines: Today And Tomorrow

Protecting Heart Health: Flu Vaccines and Beyond

Making the flu vaccine: a race against the clock


  1. Kwong et al 2018 NEJM
  2. MacIntyre CR, et al. Heart 2016;102:1953–1956. doi:10.1136/heartjnl-2016-309983
  3. Ohland et al Eurosurveillance 2020 doi: 10.2807/1560-7917.ES.2020.25.17.1900199
  4. Warren-Gash et al.Laboratory-confirmed respiratory infections as triggers for acute myocardial infarction and stroke: a self-controlled case series analysis of national linked datasets from Scotland. Eur Respir J.2018;51(3):1701794).
  5. Kalil, A.C., Thomas, P.G. Influenza virus-related critical illness: pathophysiology and epidemiology. Crit Care 23, 258 (2019).
  6. Diaco et al 2021 Vaccine
  7. last accessed September 2021
  8. last accessed September 2021
  9. last accessed September 8, 2021
  10. last accessed September 2021
MAT-GLB-2104298 v1 – 09/2021