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Does ivermectin kill the COVID-19 virus?

24 April 2020

William C. Campbell, Hon. MRIA, Ireland's only Nobel prize winner for medicine, shares his thoughts on the subject.

Professor William Cecil Campbell is a distinguished parasitologist and one of the more outstanding living scientists born and educated in Ireland. He was Senior Director of Parasitology and Director for Assay Research and Development at the Merck Institute for Therapeutic Research, New Jersey, USA, where he worked from 1957 to1990. He and his team were responsible for the discovery and development of at least six pharmaceutics, including ivermectin, which have had a huge and helpful influence on human and animal health. In 2015 he was awarded the Nobel prize in Physiology or Medicine with Professor Satoshi Omura ‘for their discoveries concerning a novel therapy against infections caused by roundworm parasites’. He was elected an honorary member of the Royal Irish Academy in 2016. We have asked Professor Campbell to share his thoughts on the effects that ivermectin may have on the COVID-19 virus and below is his response.

William C. Campbell receiving Nobel medal from King Carl XVI Gustaf, Stockholm, 10 December 2015.William C. Campbell receiving Nobel medal from King Carl XVI Gustaf, Stockholm, 10 December 2015.

It has been reported* that the antiparasitic drug ivermectin kills the COVID-19 virus (SARS CoV-2), and I have been asked repeatedly for my reaction to the report. Though destitute of expertise in virology, I will set down some thoughts on the subject, intended for a general reader. Perspective can be boring when prospects are exciting – but perspective is needed!

  1. Evidence of the lethal effect of ivermectin on the SARS CoV-2, virus has rightly been called to public attention. The report is, in itself, of great importance. “On the other hand,” the lethal effect was seen ‘in vitro’ (meaning in glass or plastic containers); and that is a long way from demonstrating such an effect in animals (in vivo tests).
  2. In this study the in vitro tests were not done by simply exposing the virus to the drug in glass or plastic containers, but rather by exposing the virus in living mammalian cells grown in such containers.  That is a much higher level of in vitro test. It is a step closer to the situation in an animal body, and that makes the evidence somewhat more encouraging with respect to potential practical use of ivermectin as an antiviral agent. “On the other hand,” the concentration of drug needed to kill the virus was many times higher than the concentration of ivermectin found in the blood of people in the normal use of ivermectin to control parasitic disease.
  3. The fact that ivermectin has been approved by the U.S. Food and Drug Administration (FDA) for use in humans has been highlighted. If future studies were to provide evidence of ivermectin anti-viral efficacy in animals, the drug’s current approval by the FDA would be enormously helpful in the conduct of clinical trials, and would thus facilitate further development toward clinical use. “On the other hand,” it has been approved for use against parasites, not against viruses; and awareness of ivermectin’s prior approval for a different use carries the risk of unduly raising hopeful expectations in this matter, with attendant risk of hasty and ill-considered action.
  4. In view of the drug concentration differential just mentioned, the probability of ivermectin being used safely to kill the virus in people must be considered low. “On the other hand,” there is, as the authors of the report point out, the possibility that a safe dosage of ivermectin might reduce the rate of viral replication in the mammalian body, or affect the virus in other ways that might be revealed by further research. That is a more positive note on which to end. 

W. C. Campbell. 9 April 2020.

William Campbell discussed the discovery and use of ivermectin in his Academy Discourse on 29 November 2017. You can listen back to his talk on our SoundCloud channel.

William Campbell's memoir, Catching the worm, will be published by the Royal Irish Academy, in partnership with the RDS, in June, to coincide with his ninetieth birthday. In his memoir, Campbell provides a snapshot of growing up in Ireland before and during World War II, as well as insights into science, the arts, teaching, family and what really matters in life. You can pre-order the book here

*Caly, L. et al. The FDA-approved Drug Ivermectin inhibits the replication of SARS-CoV-2 in vitro. doi.org/10.1016/j.antiviral.2020.104787

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