The U.S. Centers for Disease Control and Prevention said on Thursday its analysis of samples from the first severe case of bird flu in the country last week showed mutations not seen in samples from an infected backyard flock on the patient's property.

The first severe case of bird flu in the US includes unique mutations, as per CDC. These mutations, found in the patient's respiratory sample, are rare but typically seen during severe infections. The mutations may enhance the virus's ability to infect human cells but haven't been found in birds,

California’s battle with bird flu has been intensified as two new confirmed cases have been found in Stanislaus and Los Angeles counties. The rate at which the flu lathers has led California Governor Gavin Newsom to declare a state of emergency on December 18.