Dr. Anthony Fauci co-authored a paper that found masks caused most deaths during the 1918 Spanish flu pandemic.
In late July and early August 2026, social media users recirculated a rumor that Dr. Anthony Fauci, the former director of the National Institute of Allergy and Infectious Diseases, stated in a scientific paper that face masks caused most deaths during the Spanish flu pandemic in the early 20th century.
For example, on July 30, one Facebook user shared an image (archived) featuring text that claimed Fauci co-authored a paper in 2008 that found “most of the victims of the Spanish Flu didn’t die” from the illness but instead “died from bacterial pneumonia … caused by … wearing masks.” The Facebook user questioned why the physician, who helped lead the U.S. government’s COVID-19 response, “knew” this but still “recommended mask mandates.”
(Facebook user John C. Sims)
The claim recirculated primarily on Facebook. Snopes readers also contacted us to ask whether Fauci had published such a finding.
Though he did co-author a paper examining the role of bacterial pneumonia in deaths during the Spanish flu pandemic, the paper did not conclude that masks caused those infections. In fact, it did not discuss masks at all. Fauci also reportedly directly rejected the claim when the Associated Press asked him about it in 2023 (archived). As such, we have rated this claim false.
We first investigated versions of this rumor in October 2020.
What does Fauci’s 2008 paper actually say?
The paper at the center of the rumor is real. It is titled, “Predominant Role of Bacterial Pneumonia as a Cause of Death in Pandemic Influenza: Implications for Pandemic Influenza Preparedness.” It was published on Oct. 1, 2008 (not 2009, as the above Facebook user claimed), in “The Journal of Infectious Diseases.”
The researchers examined lung tissue obtained during 58 autopsies of people who died during the Spanish flu pandemic. They also reviewed pathologic and bacteriologic data from 109 published reports that included 8,398 individual autopsies. They concluded that the majority of deaths during the pandemic “likely resulted directly from secondary bacterial pneumonia” caused by bacteria commonly found in the upper respiratory tract.
The team did not conclude that masks caused those bacterial infections, as social media posts claimed. Searches for “masks” or “face coverings” on the page returned no results and the researchers made no connection between wearing masks and bacterial pneumonia.
An August 2008 news release regarding the study further explains how the bacterial pneumonia developed. Fauci said the evidence favored a scenario in which “viral damage followed by bacterial pneumonia led to the vast majority of deaths,” adding that “the virus landed the first blow while bacteria delivered the knockout punch.” The news release reads, in part:
The majority of deaths during the influenza pandemic of 1918-1919 were not caused by the influenza virus acting alone, report researchers from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health. Instead, most victims succumbed to bacterial pneumonia following influenza virus infection. The pneumonia was caused when bacteria that normally inhabit the nose and throat invaded the lungs along a pathway created when the virus destroyed the cells that line the bronchial tubes and lungs.
The authors argued that preparations for future influenza pandemics should not solely focus on influenza vaccines and antiviral drugs. They said prevention, diagnosis, prophylaxis and treatment of secondary bacterial pneumonia should also be priorities, as well as stockpiling antibiotics and bacterial vaccines. The Centers for Disease Control and Prevention similarly notes that antibiotics were not available during the 1918 pandemic to treat secondary bacterial infections associated with influenza.
In an email to the Associated Press in 2023, Fauci reportedly explained that some people with viral pneumonia also developed a secondary bacterial infection, but he added that influenza remained the underlying cause. The AP says he called the suggestion that masks were responsible “nonsense” and that there is “absolutely no evidence” masks contributed to bacterial pneumonia.
Do masks cause bacterial pneumonia?
In 2020, infectious disease specialist Davidson Hamer reportedly told the AP there is “no evidence of masks leading to fungal or bacterial infections of the upper airway or the lower airway as in pneumonia.” He added, however, that paper masks that become visibly wet should be discarded.
Doctors at Lawrence Memorial Hospital in Lawrence, Kansas, addressed the same claim that year. They said there is no evidence masks cause bacterial, fungal or viral infections of the upper or lower airway, while stressing that masks should be cleaned or replaced regularly to prevent contamination.
In 2021, Reuters also asked health scientists and infection preventionists at the Meedan Digital Health Lab about claims that masks could cause pneumonia. The experts said there is no evidence that wearing face masks increases a person’s chance of developing bacterial, fungal or viral infections in the lungs. They likewise noted the importance of keeping masks clean and using them correctly.
Studies have found bacteria on masks after they have been worn. For example, research published in 2021, 2022 and 2023 detected bacteria on used surgical, cloth and other face masks. However, those studies examined contamination of the masks and did not prove that wearing them directly caused bacterial pneumonia.
A 2014 study of hospital workers also found no indication that masks increased bacterial colonization. Bacterial colonization was lowest among workers wearing N95 respirators and highest among controls who did not routinely wear masks. The researchers concluded that N95 respirators were significantly protective against bacterial colonization.
Therefore, studies have shown that used masks can carry bacteria and should be changed or cleaned appropriately. However, finding bacteria on a mask does not mean that wearing one causes bacterial pneumonia. It was not possible to find evidence that normal mask use causes bacterial pneumonia.
Investigating 90% and 45 million figures
The Facebook post claimed that “90% of the 50 million deaths during the Spanish Flu Epidemic, didn’t die from the Spanish Flu, but from bacterial pneumonia.”
The figure of around 50 million total global deaths is consistent with CDC data (though some estimates suggest it could have killed 100 million people). The agency estimates that there were around 675,000 deaths in the United States.
However, the 2008 paper Fauci co-authored does not explicitly state that exactly 90% of the estimated 50 million people who died during the pandemic died from bacterial pneumonia. The researchers stated that evidence suggested the “vast majority” of influenza deaths resulted from secondary bacterial pneumonia. The paper did find bacteria in 92.7% of lung cultures from a group of autopsy studies. However, that figure does not represent the percentage of all pandemic deaths caused by bacterial pneumonia.
As such, Fauci’s paper does not state that 45 million people died from bacterial pneumonia. That figure appears to come from roughly applying the 92.7% figure to the 50 million deaths in the 1918 pandemic.
Bottom line
In sum, Fauci and two other researchers published a paper in 2008 that found the majority of deaths during the 1918 pandemic “likely resulted directly from secondary bacterial pneumonia.” The team did not link those infections to mask use. Instead, they linked them to the damage, caused by influenza, that allowed bacteria already present in the respiratory tract to invade the lungs. Moreover, it was not possible to find evidence that wearing face masks causes bacterial pneumonia.
