The Centers for Disease Control and Prevention on Friday urged people with weak immune systems to take extra precautions to avoid Covid after the dominant omicron subvariants knocked out a key antibody treatment.

These precautions include wearing a high quality mask and social distancing when it’s not possible to avoid crowded indoor spaces, according to the CDC.

The guidance comes after the Food and Drug Administration on Thursday pulled its authorization of Evusheld, a combination antibody injection that people with weak immune systems took as an additional layer of protection to prevent Covid infection.