A group of scientist developed Equine polyclonal antibodies (EpAbs) obtained after immunization of horses with the receptor-binding domain of the SARS-CoV-2 viral Spike glycoprotein.


Can this method of immunization serve as COVID-19 vaccine for humans?

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    Commented Sep 15, 2020 at 5:14

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This approach is not meant to yield a vaccine that will prevent infection with SARS-CoV-2. It is meant to be an antibody treatment for COVID-19.


Antibodies are infection-fighting proteins made by the immune system that can bind to the surface of viruses and prevent them from infecting cells. When a person is infected with a virus, the person makes his/her own antibodies. If all goes well, these antibodies prevent the person from being re-infected with the virus. However, it is not known with certainty that whether the antibodies produced in a person who has been infected with the SARS-CoV-2 virus will prevent re-infection and how long this protection might last.

Vaccines seek to mimic the antibody response that comes from “natural” infection with the SARS-CoV-2 virus without causing serious disease or perhaps any disease. Other yet (August 2020) unproven approaches to prevention and treatment of SARS-CoV-2 and COVID-19 involve other ways of manipulating antibodies and the immune response.


It is possible to identify and remove anti-SARS-CoV-2 virus antibodies from the blood of a person who has been infected with the virus. These antibodies can be re-infused into another person, where they would (if all goes well) modify the course of illness (make the illness less severe). The efficacy t of this kind of antibody treatment (convalescent plasma) has been evaluated in a small clinical trial in China that is described here. https://jamanetwork.com/journals/jama/fullarticle/2766940


It is also possible to “engineer” monoclonal (one specific protein) antibodies that might prevent infection with the SARS-CoV-2 virus or make the disease less severe in people who are infected and develop COVID. A number of pharmaceutical companies are trying to do this in order to make a commercially available product to prevent infection and/or treat people who develop COVID-19. This is a pre-print that describes early results of animal studies of use a monoclonal antibody “cocktail” (two different monoclonal antibodies) to modify the course of SARS-CoV-2 infection. https://www.biorxiv.org/content/10.1101/2020.08.02.233320v1


The paper cited describes a plan to use antibodies to treat COVID-19 that involves antibodies made in horses. As the authors point out, treatments based on equine antibodies have been used for decades in the management of snake, scorpion and spider envenomation and digoxin poisoning.


The authors describe immunization of horses with the receptor-binding domain of the viral spike glycoprotein of SARS-CoV-2. Plasma was collected from two horses and then digested, yielding F(ab´)2 fragments from the immunoglobulin molecules. The fragments were further purified, anofiltered (20 nm), and sterilized. The hyperimmune anti-serum will be evaluated as a therapy in patients with moderate to severe COVID-19.

This approach has been advocated as an alternative to convalescent plasma to treat COVID-19 for low and middle income countries by Stuart Ainsworth , Stefanie Menzies, Richard J. Pleass writing in June 2020.

“We therefore advocate immunization of larger animals, e.g. horses and sheep, such as is already the standard to generate antivenoms, anti-toxins, and anti-rabies therapeutics for human use. “ Page 2


Ainsworth, Menzies and Pleass go on to point out that:

“The polyclonal nature of antisera raised in animals makes it particularly suited to neutralizing multiple antigens, toxins and enzymes that in humans bitten by snakes cause coagulopathies that are also observed in COVID-19 patients.” Page 2

In the past, use of equine antibodies in humans carried a high risk of serum sickness. The use of antibody fragments has decreased this risk. There is concern about a possible adverse effect of antibody treatments, including treatments using human antibodies, on lung function in patients with COVID-19.


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