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Jeff Cercone
By Jeff Cercone January 28, 2022

Study in Brazil on ivermectin as a COVID-19 prevention is flawed, experts say

If Your Time is short

  • Experts we spoke with point out serious flaws in the study’s methodology and conclusions.

  • Health officials in Itajaí said that most residents they initially distributed the drug to did not take all five doses as recommended.

  • The FDA and World Health Organization still do not recommend the use of ivermectin in treating or preventing COVID-19 outside of clinical trials.

  • One of the study’s authors said ivermectin seemed to work  at preventing COVID-19, but he never said it was “proven.”

Ivermectin is not FDA-approved for use against COVID-19 and there’s no scientific consensus yet of its effectiveness in treating or preventing the virus. But a new study out of Brazil has advocates of the drug again proclaiming the drug’s effectiveness on social media and beyond. 

"Large, peer-reviewed research study proves ivermectin works," read the headline of a Jan. 25 article shared widely on Facebook.

The article was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

We wanted to know more about whether the study might indeed be a course-changer in the ongoing debate about using ivermectin for COVID-19. But experts in the field criticized the study as having critical flaws involving methodology and incomplete data that detract from what, if anything, it adds to the research.

The article was written by a group called the Front Line COVID-19 Critical Care Alliance, also called FLCCC, which described itself as a nonprofit organization of critical care specialists dedicated to developing prevention and treatment protocols for COVID-19. According to the group’s website, it advocates for the use of ivermectin in treating COVID-19.

One of the study’s co-authors told PolitiFact that he could not say that the research "proved" ivermectin is effective. And he said nothing replaces vaccines. Rather, the manuscript urges ivermectin as an additional tool.

Neither FDA nor WHO acknowledge ivermectin for COVID-19

Ivermectin tablets and topical forms of the drug are FDA-approved for use in humans to treat parasites and certain skin conditions, but not COVID-19. There are also animal-only formulations of the drug used to treat and prevent heartworms and other parasites. 

Asked specifically about this Facebook claim, a spokesperson for the FDA said the agency doesn’t generally comment on third-party research, but evaluates it as part of a body of evidence when forming their guidance.

And nothing about its stance has changed.

"Currently, FDA has not authorized or approved ivermectin for use in preventing or treating COVID-19 in humans," Chanapa Tantibanchachai, an FDA spokesperson wrote in an email to PolitiFact. "To date, published clinical trials have shown mixed results."

Tantibanchachai said that while ivermectin can be prescribed by doctors for COVID-19 if they deem it appropriate, "the safety and efficacy" hasn’t been established for that use and warned that the drug could negatively interact with other drugs.

The World Health Organization also still recommends against using ivermectin to treat COVID-19 outside of clinical trials. A WHO spokesperson said the organization is following the research on ivermectin.

"As of today, there is no plan to review our guidelines on ivermectin in the immediate future, but that could change," the spokesperson said.

The Brazil study 

The FLCCC story shared on Facebook links to a study published on Jan. 15 in the scientific journal Cureus. Its authors, two of whom are members of the FLCCC, concluded that "regular use of ivermectin as a prophylactic agent was associated with significantly reduced COVID-19 infection, hospitalization, and mortality rates," based on an observational study of 159,561 residents ages 18 and over in Itajaí, Brazil.

According to the study, between July 7, 2020, and Dec. 2, 2020, 113,845 participants of a citywide program took the drug, while 45,716 did not. Those who took ivermectin caught COVID-19 at a rate of 3.7%, while those who did not had a 6.6% infection rate.

After adjusting for variables, the authors said, they found a 67% reduction in hospitalization rate and a 70% reduction in mortality rate for ivermectin users.

It sounds promising, but two experts not associated with the study pointed out serious research flaws, including leaving questions about whether those identified as having taken the ivermectin actually did as prescribed. They also raised questions about conflict of interest by some of its authors.


Concerns about methodology

Dr. Nikolas Wada, an epidemiologist with the Novel Coronavirus Research Compendium at Johns Hopkins, raised concerns about the study's uncertainty over who was "truly taking ivermectin and vice versa" and poor control for factors that may predispose someone to catch COVID-19, among other issues.

"My primary takeaway," Wada said, "is that this paper adds nearly nothing to the knowledge base regarding ivermectin and COVID-19, and certainly does not prove its effectiveness as a prophylaxis."

Gideon Meyerowitz-Katz, an epidemiologist and Ph.D student from the University of Wollongong in Australia who often writes about COVID-19, said the research lacks critical information about the study’s participants, including how many Itajaí residents were already taking ivermectin before the program began and how many continued to take the full doses of the drug as prescribed.

"This sort of epidemiological study is very prone to biases resulting from characteristics that are inherently different between the intervention and control groups," Meyerowitz-Katz said. "There is essentially no information on how many people in either the intervention or control group actually took ivermectin, which is a fairly important consideration if that's what the authors were trying to investigate."

Meyerowitz-Katz detailed some of his concerns about the study in a long Twitter thread in December, when the study was in preprint, a draft version that has not been peer-reviewed. 

He said not much has changed in the published version.

The Municipal Health Department of Itajaí said in January of 2021 — a year before the study was published — that 138,216 residents took the first dose of ivermectin when it started distributing the drug as part of a citywide program. That number fell to 93,970 people taking the second and third doses, and 8,312 taking the fourth and fifth doses, the department said.

What the study’s authors say

The study’s authors acknowledged the uncertainty about the drug regimen in the "discussion" section of the publication. Dr. Flavio Cadegiani, corresponding author of the study, also addressed it in an email to PolitiFact, arguing the results would be even better in a controlled study if all users had taken the drug regularly.

But Cadegiani defended the study’s methodology.

"Limitations of the study are those inherent to any populational, observational studies," said Cadegiani, who said they used a method called propensity score matching "to increase the level of certainty of the findings."

Cadegiani said that in addition to showing positive results for ivermectin, the study explicitly states that "nothing replaces the vaccines."

Dr. Lucy Kerr, the study’s lead author, responded to criticism in the comment section below the study, writing that the data was complete and that "the most relevant clinical variables that affected mortality from COVID-19 were considered. She said that the study was "strong, robust, precise" and "very high quality."

We reached out to Kerr via email but didn’t hear back.

As for whether the headline of the article’s assertion that the study "proves" that ivermectin works, even Cadegiani isn’t so sure, despite being a member of the FLCCC, the group promoting the study.

"Our work was to check whether in that population ivermectin would be effective or not, in terms of protection from COVID-19 infection, hospitalizations, or deaths. At least from what we received, it seemed to work. And I was not a believer at all," he told PolitiFact.

"Now, the concept of being 'proven' is scientifically hard to tell — even a precise definition lacks," he said. "I have never said it was proven anywhere. How people interpret and claim, that is not under my control."

Conflicts of interest concerns

Wada and Meyerowitz-Katz, who were not involved with the study, each pointed out potential conflicts of interest with the study’s authors. They noted that although the preprint version of the study mentions that two of its authors received money from a pharmaceutical company that manufactures ivermectin, the published version leaves that detail out.

The preprint study said that Kerr received funding from Vitamedic "unrelated to this study" and that Cadegiani was paid for consulting services by the firm, also unrelated to the study, and that he donated it all for COVID-19 patient care and research. In an email to PolitiFact, Cadegiani also said he did not have any conflicts and reiterated that he had donated his payment.

The published version of the study simply stated that "all authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work."

The National Research Ethics Commission in Brazil, meanwhile, is investigating another clinical trial of an experimental COVID-19 drug in which Cadegiani was the lead author for possible violation of ethics, according to The BMJ and the publication Science.

Our ruling

An article shared on Facebook about an ivermectin study out of Brazil states that the "large, peer-reviewed research study proves ivermectin works." The article is being promoted by the Front Line COVID-19 Critical Care Alliance, a group that promotes the use of ivermectin to treat COVID-19. Two of the study’s authors are members of the group.

The study, one of its authors said, does not definitively prove that ivermectin works as a prevention or treatment for COVID-19.

Experts not involved in the study pointed out serious flaws in the study and conflicts of interest with its authors. The FDA and WHO have not changed their positions on the use of ivermectin outside of clinical trials.

We rate this claim False.

Our Sources

Email interview with Dr. Flavio Cadegiani, corresponding author of the ivermectin study, Jan. 28, 2022

Email from Chanapa Tantibanchachai, FDA spokesperson, Jan. 25, 2022

Email from World Health Organization spokesperson, Jan. 26, 2022

Email interview with Gideon Meyerowitz-Katz, an epidemiologist and Ph.D. student at the University of Wollongong in Australia, Jan. 26, 2022

Email interview with Dr. Nikolas Wada, an epidemiologist with the Novel Coronavirus Research Compendium at Johns Hopkins, Jan. 26, 2022

Clinicaltrials.gov, "Find a study"

Health Feedback, "Ivermectin study in the city of Itajaí contains several methodological weaknesses, resulting in questionable conclusions," updated Jan. 25, 2022

Lead Stories, "Fact Check: Hospitalizations, Mortality Were NOT Cut In Half After Brazilian City Offered Ivermectin; City Officials Rebut Study," Dec. 14, 2021

The FLCCC Alliance, "Large, peer-reviewed research study proves ivermectin works," Jan. 20, 2022

The FLCCC Alliance, "Ivermectin in COVID-19"

The FLCCC Alliance, "Mission statement and objectives"

Cureus, "Ivermectin Prophylaxis Used for COVID-19: A Citywide, Prospective, Observational Study of 223,128 Subjects Using Propensity Score Matching," Jan. 15, 2022

ResearchGate, "Ivermectin Prophylaxis Used for COVID-19 Reduces COVID-19 Infection and Mortality Rates: A City-Wide, Prospective Observational Study of 223,128 Subjects Using Propensity Score Matching." Preprint version

FDA, "Why You Should Not Use Ivermectin to Treat or Prevent COVID-19," Dec. 10, 2021

Infectious Diseases Society of America, "Ivermectin recommendations," Aug. 10, 2021

Open Forum Infectious Diseases, "Ivermectin for COVID-19: Addressing Potential Bias and Medical Fraud," Jan. 17, 2022

The News & Observer, "Ivermectin’s potential to treat COVID gets a serious look in Duke University study," Jan. 20, 2022

PolitiFact, "Fact-checking claim about the use of ivermectin to treat COVID-19," April 23, 2021

PolitiFact, "A Nobel Prize and a horse dewormer: Explaining the controversy over ivermectin and COVID-19," Sept. 8, 2021

Science, "‘Too good to be true': Doubts swirl around trial that saw 77% reduction in COVID-19 mortality," July 7, 2021

World Health Organization, "Therapeutics and COVID-19: Living Guideline, Ivermectin," March 31, 2021

The Municipal Health Department of Itajaí, "Note of clarification - prophylactic treatments," Jan. 21, 2021

NIH, "COVID-19 treatment guidelines, ivermectin," Feb. 11, 2021

The BMJ, "Covid-19: Trial of experimental "covid cure" is among worst medical ethics violations in Brazil’s history, says regulator," Nov. 17, 2021

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Study in Brazil on ivermectin as a COVID-19 prevention is flawed, experts say

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