By Jamie Gumbrecht, CNN

(CNN) -- The US Food and Drug Administration on Thursday halted the emergency use authorization of Evusheld because it does not appear to protect against Covid-19 from viral variants currently circulating in the United States.

Evusheld is a monoclonal antibody therapy used to prevent Covid-19 in immunocompromised people, who are less likely to generate an immune response from Covid-19 vaccination.

US officials have warned for months that the antibody therapy was not working against certain emerging variants, but it was still available. CNN had previously reported that many patients who used the medication weren't aware the medication was no longer as effective as it once was, and continued to rely on it for protection against Covid-19.

On Thursday, the FDA revised Evusheld's emergency use authorization to limit it to when the combined frequency of non-susceptible coronavirus variants is less than or equal to 90%.

Data has shown Evusheld is unlikely to work against XBB, XBB.1.5, BQ.1 and BQ.1.1; combined, these variants are estimated to be causing nearly 93% of new US Covid-19 cases.

"This means that Evusheld is not expected to provide protection against developing COVID-19 if exposed to those variants," the FDA said in a statement Thursday.

The agency said that if someone becomes infected and develops Covid-19 symptoms, they should seek medical care and may be able to use antivirals Paxlovid, remdesivir or molnupiravir, all of which work against currently circulating variants.

Several antibody therapies used against Covid-19 earlier in the pandemic are no longer available because the virus has evolved and they are no longer effective. AstraZeneca, the maker of Evusheld, said in a statement that it is investigating the safety and efficacy of a "next-generation long-acting antibody" to prevent Covid-19 among immune-compromised people.

Although Evusheld isn't authorized for now, the FDA said providers should hold on to the medicine.

"The U.S. Government recommends that facilities and providers with Evusheld retain all product in the event that SARS-CoV-2 variants which are neutralized by Evusheld become more prevalent in the U.S. in the future," the agency said.