No evidence that flu shot increases risk of COVID-19

By 27/04/2020January 5th, 2021No Comments

By FactCheck.org

Quick Take

A claim being pushed on social media and by an organization skeptical of vaccines is using a military study to falsely suggest that the flu vaccine increases someone’s risk of contracting COVID-19. The study does not say that, and the Military Health System advises people to get the flu shot.

Full Story 

Federal health officials are warning that the novel coronavirus outbreak could resurge in the fall, presenting a significant public health quandary: fighting both COVID-19 and the flu at the same time.

Robert Redfield, director of the U.S. Centers for Disease Control and Prevention, noted the importance of the flu vaccine in controlling the spread of influenza in a recent interview with the Washington Post. He said the flu shot “may allow there to be a hospital bed available for your mother or grandmother that may get coronavirus.”

But social media posts are singing a different tune, cautioning against the flu shot by falsely suggesting that the vaccine increases the chances of getting COVID-19 by “36%.”

The argument is being pushed in a post by Children’s Health Defense — an organization founded by Robert F. Kennedy Jr., known for his vaccine skepticism — headlined “Pentagon Study: Flu Shot Raises Risk of Coronavirus by 36% (and Other Supporting Studies).” The post, republished elsewhere, pointed to “peer-reviewed, published studies” to “prove” that advice offered by CNN anchor Anderson Cooper in March for people to get the flu shot “may have been the worst advice he could have given the public.”

That’s wrong.

First of all, experts say there has been no study connecting the flu shot with an increased risk of SARS-CoV-2, the novel coronavirus that causes COVID-19.

The central study cited by the Children’s Health Defense is a 2019 Armed Forces Health Surveillance Branch study that probed the theory that “influenza vaccination may increase the risk of other respiratory viruses” — a concept known as “virus interference.”

Edward Belongia, an infectious disease epidemiologist at the Marshfield Clinic Research Institute, told us that the theory rests on the idea that “if you get a flu infection, for example, maybe for some period of time your immune response to that flu infection reduces your risk of getting infected by some other virus.”

Belongia said virus interference has been the subject of speculation and some studies with mixed results, but there is ultimately little data to support it. A 2013 study he worked on, cited in the AFHSB study, found that “influenza vaccination was not associated with detection of noninfluenza respiratory viruses.”

In fact, the AFHSB study concluded that its “overall results … showed little to no evidence supporting the association of virus interference and influenza vaccination.”

The erroneous claim that the study shows a heightened risk for COVID-19 for those vaccinated for the flu hinges on the study’s suggestion that vaccinated individuals appeared more likely to get “coronavirus.”

But the study looked at four types of seasonal coronaviruses that cause common colds, not SARS-CoV-2.

What’s more, Belongia said, the results in the study that indicate a flu-vaccinated person has an increased likelihood of testing positive for a seasonal coronavirus do not appear to be adjusted for age groups or seasons. Those factors could affect someone’s chances of getting a specific virus, regardless of whether or not they’ve been vaccinated for the flu.

Different viruses affect different age groups and circulate at different times, he said. “It can be easily explained just by random variation and the fact that they didn’t adjust for confounding variables.”

The Military Health System, of which the AFHSB is a part, noted in a statement to FactCheck.org that the study used data collected two years before the emergence of COVID-19 and looked at the seasonal coronaviruses — “impacting children and adults with no serious complications” — which “do not have the potential for epidemic or pandemic spread.”

“The study does not show or suggest that influenza vaccination predisposes in any way, the potential for infection with the more severe forms of coronavirus, such as COVID-19,” the MHS said.

Furthermore, the statement said, “it’s also important to note the study found evidence of significant protection by influenza vaccination against not only multiple forms of the flu, but other, very serious non-influenza viruses, such as parainfluenza, Respiratory Syncytial Virus (RSV), and non-influenza virus coinfections. It remains essential for people to obtain the seasonal flu shot each year as it becomes available.”

There have been some results suggestive of virus interference, which the Children’s Health Defense cites in its post. But none of the studies referenced assessed risks of the flu shot when it comes to COVID-19.

For example, Sharon Rikin, an assistant professor of medicine at Albert Einstein College of Medicine and Montefiore Medical Center, said in an email that a 2018 study she worked on “showed an association with flu vaccination and a slightly higher risk of non-flu acute respiratory infections (such as the common cold) in children. However, this association was not seen in adults.”

“In medicine, we are always weighing the risks and benefits of treatments. In this case, we know that the flu vaccine is safe and effective to reduce illness and death among children and adults every year,” Rikin added. “We have not studied the association between flu vaccination and risk of COVID-19. Fortunately, COVID-19 is typically not causing significant illness in children. However, preventing illness and death from flu still remains extremely important for children.”

Rikin said “just because we found an association between flu vaccines and acute respiratory infections does not mean that the flu vaccine actually caused there to be a higher risk of infections.” She said the group struggled to find a “biologically plausible explanation” and that while “there is a small body of literature that hypothesizes that the phenomenon of shifts in viral prevalence could be caused by viral interference,” there is not “strong empirical evidence of this occurring.”

Belongia told us that, ultimately, the evidence of virus interference through such studies “is weak and inconclusive.”

“Overall, we do not see evidence of virus interference that is sufficient to raise concerns about flu vaccination and COVID-19 risk,” he said. “Serious COVID-19 disease occurs primarily in adults, and we do not have evidence of flu vaccine causing virus interference in adult age groups.”

He said that getting the flu shot, if anything, is especially important because of potential problems posed by the combination of the flu and COVID-19, both for the health care system and individuals.

Likewise, Richard Ellison, a professor of medicine at the University of Massachusetts Medical School and hospital epidemiologist at UMass Memorial Medical Center, told us in an email that “getting the flu itself carries very significant morbidity and potentially mortality — so we don’t want someone to get the flu in the first place.”

“In addition, while having the flu may boost the immune system, it can significantly weaken someone’s overall health status, and make them more susceptible to complications should they be unfortunate enough to have both influenza and COVID-19 in the same year.”

Update, April 27: We removed a reference to a 2017 study, which was cited by the Children’s Health Defense, and a quote from one of its authors, because the study’s methodology and veracity have been disputed.

Editor’s note: FactCheck.org is one of several organizations working with Facebook to debunk misinformation shared on social media. Our previous stories can be found here.


Belongia, Edward. Director, Center for Clinical Epidemiology & Population Health, Marshfield Clinic Research Institute. Email and phone interview with FactCheck.org. 24 Apr 2020.

Ellison, Richard. Hospital epidemiologist, UMass Memorial Medical Center. Email to FactCheck.org. 23 Apr 2020.

Military Health System. Email statement to FactCheck.org. 24 Apr 2020.

Remarks by President Trump, Vice President Pence, and Members of the Coronavirus Task Force in Press Briefing.” White House. 22 Apr 2020.

Rikin, Sharon. Assistant professor of medicine, Albert Einstein College of Medicine and Montefiore Medical Center. Email to FactCheck.org. 24 Apr 2020.

Sun, Lena H. “CDC director warns second wave of coronavirus is likely to be even more devastating.” Washington Post. 21 Apr 2020.

Wolff, Greg G. “Influenza vaccination and respiratory virus interference among Department of Defense personnel during the 2017–2018 influenza season.” Vaccine. Vol. 38, Issue 2. 10 Jan 2020.