Fact check: Chloroquine/SARS study does not prove hydroxychloroquine’s effectiveness against COVID-19

Posts circulated on social media make the claim that the results of a 2005 chloroquine/SARS study provide evidence of hydroxychloroquine’s effectiveness against COVID-19. This is false.

Reuters Fact Check. REUTERS/Axel Schmidt

Some posts on social media contain screenshots of a 2005 study originally published in the Virology Journal ( here ) and found among the National Institutes of Health’s archived studies ( here ). The original article is entitled “Chloroquine is a potent inhibitor of SARS coronavirus infection and spread”.

Other posts are accompanied by screenshots of an April 2020 opinion column by Bryan Fischer on “The Northwest Connection” ( ). Fischer referenced the same Virology article and notably wrote: “So HCQ functions as both a cure and a vaccine.” Examples of the claim are visible here and here .

The 2005 study in Virology specifically found that chloroquine had “strong antiviral effects on SARS-CoV infection of primate cells,” and that “favorable inhibition of virus spread was observed when the cells were either treated with chloroquine prior to or after SARS CoV infection” meaning that the drug had both preventative and therapeutic benefits for the test subjects.

This study, however, was limited to animal testing in a laboratory setting (the study refers to primates in its abstract and methodology, there is no mention of human testing, pages 1 and 9 here ). The authors do suggest that their positive results in primate cell culture are promising (see page 9) and the use of chloroquine for the clinical management of SARS is presented as a possibility. They also mention that “infectivity of coronaviruses other than SARS-CoV are also affected by chloroquine, as exemplified by the human CoV-229E” (page 9), a possible source for the online claims.

The study’s focus was the then-newly discovered SARS-CoV coronavirus that causes Severe Acute Respiratory Syndrome, not the SARS-CoV-2 that causes COVID-19. While the two are both coronaviruses, they are different strains causing different diseases.

The 2005 study could not have investigated chloroquine’s effectiveness against SARS-CoV-2 because the latter was not identified until January 2020 following the December 2019 outbreak in Wuhan, China, of what we now know as COVID-19 ( here ).

Chloroquine and hydroxychloroquine are two related, but different drugs with similar “clinical indications for use” and similar toxicity ( here ).

As of this fact check’s publication, evidence for chloroquine and hydroxychloroquine’s effectiveness against COVID-19 remains inconclusive.

As of June 16, 2020 the U.S. NIH recommends against the “use of chloroquine or hydroxychloroquine for the treatment of COVID-19, except in a clinical trial” and against “the use of high-dose chloroquine (600 mg twice daily for 10 days) for the treatment of COVID-19.” ( here )

On July 1, the U.S. Food and Drug Administration (FDA) also cautioned against the use of hydroxychloroquine or chloroquine for COVID-19 “outside of the hospital setting or a clinical trial due to risk of heart rhythm problems.” ( here )

This warning did not discourage the use of these drugs for FDA-approved uses for other diseases like malaria, lupus, and rheumatoid arthritis.

Another recent study published in the International Journal of Antimicrobial Agents found that unsupervised use of chloroquine or hydroxychloroquine as a preventive measure against COVID-19 can “expose the public to serious adverse drug effects” ( here ).

In June, the World Health Organization (WHO) discontinued experimental treatments involving the use of hydroxychloroquine and lopinavir/ritonavir after the initial results of an international trial called Solidarity showed that the drugs produced little or no reduction in the mortality of hospitalized COVID-19 patients ( here , here ).

One month earlier, EU governments moved to halt the use of anti-malaria drug hydroxychloroquine to treat COVID-19 patients, Reuters reported. Medicines agencies in France and Italy said the drug should not be used for COVID-19 outside clinical trials. Belgium’s regulator said trials aiming to evaluate the drug should also take potential risks into consideration ( here ).


False. A 2005 chloroquine/SARS study does not prove hydroxychloroquine’s effectiveness against COVID-19. Existing evidence on the drug’s effectiveness against COVID-19 remains inconclusive.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here .