There is a saying that when all you have is a hammer, everything looks like a nail.

So, it should come as no surprise that vaccine skeptics worldwide are sounding the alarm about the flu shot as a real danger in the COVID-19 pandemic.

Confused? Well, it turns out the anti-vaccine activists are too.

In the Beginning, There was Misunderstanding: The Genesis of a Myth

One of the earliest reports suggesting a link between influenza vaccination and an increased risk of COVID-19 was published by the Children’s Health Defence on their website. The article claims that people vaccinated against seasonal influenza have a 36% higher risk of coronavirus infection. While the original story does not specifically mention SARS-CoV2 – the coronavirus responsible for COVID-19 – social media posts by Children’s Health Defence explicitly connect influenza vaccines and a greater risk of COVID-19. At best this is a misunderstanding of a few research studies, and at worst it is a misrepresentation designed to advance a self-serving narrative.

The Misleading Case Against Vaccination

How do anti-vaccine organizations make a connection between flu shots and COVID-19? Two small studies by Wolff and Cowling et al found evidence showing that there may be a short-term increase in the risk of coronavirus infection following influenza vaccination. However, in a larger, multi-year follow-up study, these findings were unable to be replicated. Moreover, none of these studies examined the impact of influenza vaccines on SARS-CoV2, the coronavirus that causes COVID-19. Interestingly, Dr. Gregg Wolff – the author of one of the studies reporting a link between coronavirus infections and influenza vaccination – published a letter disputing the claims made by Children’s Health Defense about his research, and argued that flu shots are overwhelmingly positive.

In short, none of these commonly cited studies support or even address the claim that the flu shot increases the risks associated with COVID-19.

Dismantling Misinformation

Despite the relatively recent appearance of COVID-19, a handful of studies have already examined claims by vaccine skeptics that the flu shot increases the risk for COVID-19. It turns out the results aren’t what anti-vaccine advocates advertise.

In the earliest days of the COVID-19 pandemic, mortality rates skyrocketed in Italy. Rates were highest in older individuals, which is consistent with worldwide trends that identified this cohort as being at high risk. For reasons that are not clear, a hypothesis was generated linking high mortality rates with an influenza vaccination program that occurred in Italy the previous fall.

However, almost as quickly as the mythical link was proposed, science began to uncover evidence that convincingly crushed the connection. Researchers from Weill Cornell Medicine in New York City published a letter in the Journal of Medical Virology noting that an analysis of vaccination patterns across Italy showed regions with higher influenza vaccination levels had lower COVID-19 mortalities, specifically in adults aged 65 years or older.

A systematic review of 7 studies comprised of 242,323 people across Italy, Germany, USA, and Spain found similarly positive links between the flu shot and COVID-19 outcomes. Overall, the studies found that the risk for SARS-CoV2 infection was lower in individuals who were vaccinated against influenza, and that severity of COVID-19 was lower for those who were infected. One study reported lower mortality rates in COVID-19 patients who were vaccinated, while 2 found no significant differences. Similar to the report by researchers at Weill Cornell Medicine, these studies found that the greatest benefits were seen in the high risk >65 year old cohort.

Together these studies clearly show that not only is the influenza vaccine not a risk for COVID-19, it may offer significant benefits.

The Cherry On Top

One concerning trend that emerged early in the pandemic and has been repeatedly validated is the involvement of the cardiovascular system in COVID-19. Individuals with pre-existing cardiovascular conditions like coronary artery disease and high blood pressure are at higher risk of severe illness or death from SARS-CoV2 infection. Additionally, damage to heart muscle and blood vessels are well documented in COVID-19 patients, and are a significant cause of death. Protecting the cardiovascular system and limiting damage from other viruses like influenza is critical to improving the outcome of COVID-19 patients.

It turns out that in addition to preventing influenza infection, the flu shot protects the heart. In elderly patients, vaccination decreases the risk of heart attack or stroke by ~20%. In patients with existing heart failure, influenza vaccines decrease hospitalization by almost 30%.

For patients without diagnosed cardiovascular disease but who have cardiovascular risk factors like diabetes, the influenza vaccine still offers significant benefits. A 2020 study followed 241,551 patients with diabetes over 10 years. Not only was influenza vaccination associated with a reduced risk of hospital admissions for diabetes complications, it decreased the chances of dying from a heart attack or stroke. In COVID-19 patients, diabetes is a risk for severe illness and death. The cardioprotective benefits of an influenza vaccine could reduce the stress placed on the cardiovascular system and improve outcomes for diabetics infected with SARS-CoV2.

Like any vaccine, the flu shot is not 100% effective. However, even when the vaccine does not prevent infection, it can still reduce the severity of illness and decrease cardiovascular complications. Chiang and colleagues reported that after influenza vaccination, elderly patients who experienced an influenza-like illness were less likely to suffer major cardiovascular events than unvaccinated individuals.

The Big Picture

Vaccination opponents have taken to social media to present their case to the public, arguing that vaccines are unsafe and ineffective. Despite their vocal and persistent claims, the scientific evidence is overwhelmingly against them. Countless studies and trials demonstrate the safety of vaccines, and research convincingly shows that not only do vaccines offer benefits by decreasing infections, they protect against complications.

Myths and distortions about the flu shot have collided with misconceptions and deceptions about COVID-19 to create an epidemic of misinformation. While reports of potential COVID-19 vaccines offer hope for tackling the coronavirus pandemic, there is no sign of end to the dangers of viral propaganda about medical science, which is a real threat to global health.