The Food and Drug Administration (FDA) said on Friday that AstraZeneca’s preventative monoclonal antibody treatment for COVID-19 is likely ineffective against the XBB.1.5 omicron subvariant due to its similarity to other mutations of the virus that are also not neutralized by the treatment.

In a statement, the FDA said it “does not anticipate that Evusheld will neutralize XBB.1.5.”

“This means that Evusheld may not provide protection against developing COVID-19 for individuals who have received Evusheld and are later exposed to XBB.1.5,” said the agency. “However, we are awaiting additional data to verify that Evusheld is not active against XBB.1.5. We will provide further updates as new information becomes available.”

Evusheld is a combination of two monoclonal antibodies that has been authorized as a pre-exposure prophylaxis to prevent COVID-19 infections in those who are moderately to severely immunocompromised.

The treatment was also recommended for use in people who may not be good candidates for coronavirus vaccination or those who have history of developing adverse reactions to COVID-19 shots. The Centers for Disease Control and Prevention also previously recommended Evusheld to be administered in immunocompromised people who have been vaccinated as a supplement the vaccine’s protection.

Evusheld is currently the only authorized available option for pre-exposure prophylaxis in immunocompromised individuals who may not develop a strong enough immune response from vaccination alone.

The FDA advised health care providers to inform their patients of the increased risk of COVID-19 infection due to variants that are not neutralized by Evusheld.

The XBB.1.5 subvariant accounts for about 2 percent of COVID-19 cases in the U.S. as of this week, with most cases in the Northeast now attributed to this mutation. Health officials have stated that XBB.1.5 appears to evade immune protection better than previous subvariants, with some calling it the most transmissible subvariant that has been detected so far.

While Evusheld is likely ineffective against preventing infection from XBB.1.5, officials from the White House have said that the bivalent COVID-19 booster dose as well as the antivirals like Paxlovid are likely still effective at treating cases brought on by the subvariant as well as reducing the chances of severe illness.