On May 2, 2025, CDC published a new IRAT assessment for two clade 2.3.4.4b avian influenza A(H5N1) viruses: A/California/147/2024 and A/Washington/239/2024. These are two viruses that caused recent human illnesses in the United States.

Summary: The overall pandemic risk posed by these two viruses has not changed significantly and remains "moderate."

The A/California virus is a representative B3.13 genotype virus; these viruses are currently causing outbreaks in dairy cows in the United States and associated with sporadic human illnesses, mostly among those who had exposure to A(H5N1) virus-infected or presumed infected dairy cattle.
A/Washington is a representative D1.1 genotype virus; these viruses are currently circulating in wild/migratory birds and have been associated with human illnesses, mostly among people who had exposure to poultry confirmed to have A(H5N1) virus infection. The genes of this virus are more closely associated with the viruses that have been most commonly spreading in U.S. wild birds and poultry.
The A/California/147/2024 and A/Washington/239/2024 viruses scored similarly to three previous avian influenza A(H5N1) clade 2.3.4.4b viruses assessed previously using the same method. The findings of this report indicate that developments through March 14, 2025, have not significantly changed the potential pandemic risk (for either emergence or impact) posed by avian influenza A(H5N1) clade 2.3.4.4b viruses, which continues to be moderate. The results of this IRAT confirm that this outbreak poses a moderate potential public health risk and validates the proactive, coordinated U.S. government response.