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Regeneron said Tuesday that its monoclonal antibody cocktail prevented Covid-19 in a clinical trial.

The news, issued via a press release, mirrored similar news from Eli Lilly last week that its monoclonal antibody prevented symptomatic Covid-19 infections in nursing homes.

The results represent the first 400 volunteers from the study, which is being run by the National Institute of Allergy and Infectious Diseases (NIAID), and is continuing to enroll patients. The volunteers were at high risk of infection because they lived in the same household as a Covid-19 patient. Half the patients received a placebo, and the other half received 1.2 grams of casirivimab and imdevimab, Regeneron’s antibodies.


While eight of the 223 patients in the placebo group developed Covid symptoms and tested positive for the virus, none of the 186 patients who received the antibody did. Volunteers who received the antibody were also less likely to be asymptomatic carriers of the SARS-CoV-2 virus, which causes Covid-19. Twenty-three volunteers in the placebo group tested positive for the virus, compared to 10 in the antibody group, a 50% reduction.

It also appeared that infections in volunteers who received the antibody were less severe than those who did not, the company said. Infected volunteers in the placebo group had on average, more than 100-fold higher peak viral loads. Infections in the antibody group lasted no longer than a week, while 40% of the infections in the placebo group lasted three to four weeks.


Adverse events were less common among those who received the antibody cocktail, occurring at 18% in the placebo group and 12% in the antibody group. This was the result of the negative effects of the virus. Two percent of those in both groups had injection site reactions.

George Yancopoulos, Regeneron’s chief scientific officer, said in a statement that even with vaccines available, the antibody will be able help break the chain of infection, and may prove useful for individuals who are immunocompromised or unable to be vaccinated.

Regeneron was able to formulate the antibody so that it could be given as an injection, instead of being given intravenously. That would make the antibody much easier for health care workers to give.

The results have not been peer-reviewed or published in an academic journal.

  • I received the Regeneron Antibody Cocktail in December… I tested for Covid on December 6th and got my results on December 8th… I was offered the Regeneron Cocktail infusion on December 10th… My Covid symptoms never got any worse but in turn started to get better in 24hours… I am so thankful for the hard work to make this treatment available… I am a 59 year old male with many underlying health conditions… If you get Covid and have the opportunity to receive the Regeneron Antibody infusion… Get it… It could save your Life…

  • Anecdotally, we are seeing similar very positive outcomes for those patients we have guided to regional hospitals for this treatment (monoclonal antibodies) through Covid Plasma Initiative, a non-profit I volunteer for. We have guided close to 100 patients in the last few weeks alone, helping them figure out if they qualify etc. We were encouraged by the possibility for patients to access the treatment through the Regeneron trials, since some of those patients cannot get them under the current risk criteria (which is still fairly limited).

  • I received the monoclonal antibody infusion. I received the infusion the first day I had some problems breathing. I have been told I should not get the vaccine for 90 days from onset of Covid. I am concerned about the new strain of the virus and if it will have any effect on the monoclonal antibody infusion How long should the infusion be effective? I am concerned because I am 86 and have NTM.
    Should I be tested for antibodies? I am very concerned that I will be confined to my house while everyone I know has gotten the vaccine. Am I safe for awhile?

  • Please consider necessity of monoclonal Ab therapy in view of emerging strains which may render current vaccines less effective. This therapy can be a lifeline if used early in a “hot spot” such as nursing homes. Needs to be available ASAP. Death numbers way too high still. Public needs to see this is all out effort, to keep new enthousiasm and momentum up. Thanks

  • Regeneron is making 1.5 million injectable doses before June 30 this year for two contracts from the US government. Regeneron is working with Roche on production of 2 million doses per year, with development and distribution by Regeneron in the US, and by Roche outside the US. This is quite solid prevention and treatment progress, and may need to be stepped up as vaccine roll-out is encountering supply problems.

  • I am very glad to see this kind of progress in a preventive treatment. The way things are going, I’m not sure vaccination will ever be a solution, since they can’t make enough, get enough people injected, and because the virus keeps on and will keep on mutating into heaven only knows what. This treatment appears to be broad spectrum – at least at present – though this virus seems to keep on defying historical expectations, despite the patently false claim by so many medical authorities that “all viruses do this.” Really? Because looking back, that doesn’t seem to be the case.

  • Does this mean that we can replace vaccine with antibodies ? How long will these antibodies last ?

    Is this safer than the vaccine? Meaning are these antibodies created on the lab or derived from patients plasma. If derived from patient plasma, what is the check that the antibodies solution does not carry other diseases.

  • Why isn’t it given to everyone then. I believe it’s true, so why are so many people dying that could have been saved. Trump and his friends got it and were curedcof Covid19 in 3 days. Why not everyone?

    • Because it’s currently an infusion, it’s tough to adminster outpatient (though the article says they’ve reformulated it to be a shot). There are a few infusion sites set up in Las Vegas, El Centro and other cities, but not many. If you can’t find one of those, call your ER to find out if they have it and do it there. My friend did this for her elderly mom (forewarning–it won’t be easy, she was on the phone for hours finding an ER that had it and would give it to her mom). Also, the antibodies are still in short supply (why they haven’t been pushing it), but they aren’t being used and are just sitting on the shelves. Use them. Use them in the first 3 or so days of infection or they won’t help that much. Also, I just want to remind everyone that Trump received an 8g dose of this antibody cocktail, much higher than the 1.2g dose in this trial.

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