(Bloomberg) -- Regeneron Pharmaceuticals Inc.’s antibody treatment for Covid-19 received U.S. regulators’ blessing as the first preventative therapy for unvaccinated and immunocompromised people in high-risk settings.

The decision by the Food and Drug Administration expands an emergency use authorization, first granted in November, for the antibody cocktail to treat mild to moderate Covid infections in people 12 years old and up. It allows Regeneron to offer the combination of casirivimab and imdevimab, called REGEN-COV, in more contexts to more patients in the same age group. The treatment still hasn’t been cleared for patients hospitalized with Covid.

Antibody therapies are among the few treatments proven effective against Covid infections, but they’re usually administered at infusion centers and the price tag can be hefty. The FDA’s decision to allow Regeneron’s therapy as a measure for people who have been exposed to Covid could be a milestone for prevention of severe infections in high-risk individuals.

To be eligible, patients must have both a high risk of developing more severe disease from Covid -- either because they’re unvaccinated or have a weak immune system -- and have a good chance of getting infected because of exposure. One example could be someone living in a congregate space where they’ve been exposed to a Covid-infected person. Regeneron said its therapy can also be used across multiple months if exposure continues for a longer period.

While the company said REGEN-COV isn’t a substitute for vaccines, inoculations may not be as effective for people with weak immune systems. In such cases, Regeneron said, its therapy could be used to complement shots. The antibody treatment could also be used in outbreaks where immediate protection is needed, since Covid vaccines take about two weeks to become fully active against the virus.

Though the therapy can be used for more than a month at a time in certain cases, it hasn’t been approved yet for even broader preventative use among the immunocompromised. Discussions about such an expansion are ongoing, Regeneron said.

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