NEW YORK (CNN) — A medicine that may treat and prevent COVID-19 is now being tested in patients in multiple sites around the United States, according to an announcement Thursday from Regeneron Pharmaceuticals Inc.

It is the first trial of a COVID-19 antibody cocktail in the United States. If successful, Regeneron hopes it could be available by the fall.

The clinical trial started Wednesday. Regeneron said its antibody cocktail will be tested in four separate study populations: people who are hospitalized with COVID-19; people who have symptoms for the disease, but are not hospitalized; people who are healthy but are at a high risk for getting sick; and healthy people who have come into close contact with a person who is sick.

"We have created a unique anti-viral antibody cocktail with the potential both to prevent and treat infection, and also to preempt viral 'escape,' a critical precaution in the midst of an ongoing global pandemic," Dr. George Yancopoulos, co-founder, president and chief scientific officer at Regeneron, said in a press release. "Ultimately, the world needs multiple solutions, and the innovative biopharma industry is collectively working hard to help as many people as possible with a variety of complementary approaches."

Antibodies are proteins the body naturally makes to protect the body from a threat like COVID-19. To make what's called monoclonal antibodies for an antibody cocktail, scientists comb through thousands of antibodies to figure out which ones fight the novel coronavirus most effectively.

In this case, Regeneron's scientists picked two antibodies, scaled them up and put them into a medicine that it hopes can be used to treat symptoms or and as protection for vulnerable communities such as the elderly or health care workers.

The first part of the trial will check to see if the antibody therapy is safe to be used in humans. Scientists will also want to if it works.

An antibody treatment is not a vaccine and does not provide permanent protection. But this kind of passive immunization works right away, and could potentially be available before a Covid-19 vaccine.

More antibody treatments in trials

Regeneron is not the first company to get a COVID-19 antibody therapy into human trials.

Eli Lilly and AbCellera started testing their antibody treatment in humans June 1. That trial uses a single antibody in its therapy. Eli Lilly has also started a second clinical trial in China of another single antibody treatment it created with Chinese company Junshi Biosciences.

Eli Lilly said that they will test combinations of antibodies in the future.

There are a handful of other companies working on additional antibody therapies. Tarrytown, New York-based Regeneron has successfully created other U.S. Food and Drug Administration-approved antibody therapies that fight eye problems, rheumatoid arthritis, cancer and cardiovascular disease.

Regeneron's Ebola treatment worked so well, its clinical trial was stopped early in August 2019. Data showed it was better at saving lives than some of the other therapies being tested. The FDA accepted REGN-EB3 for priority review in April. The agency is expected to make a decision about whether to OK the Ebola therapy by October.

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Regeneron scientists said they had spent years preparing for a pandemic like COVID-19.

"Most scientist have said for years there's potential for pandemics like this novel coronavirus to emerge," Regenron scientist Kristin Pascal previously told CNN. "So we thought, let's be prepared."

To get ready, Pascal and her team ran speed challenges to see exactly how fast they could create a treatment for an emerging threat. They did it for MERS and Ebola and they hope all that practice will pay off against Covid-19.

The company, which some financial backing from the U.S. Biomedical Advance Research and Development Authority to develop the COVID-19 therapy, said it set a company speed record by creating REGN-COV2 in months.

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