Update on CDC’s Avian Influenza A(H5N1) “Bird Flu” Response Activities
CDC continues to respond to the outbreak of H5N1 bird flu in poultry and dairy cows in the United States. Recent CDC activities include a ferret study that showed an avian influenza A(H5N1) virus from a human case in Michigan causes less severe disease than the Texas human case virus, outreach to farm workers in affected counties through local radio station advertisements that provide information in English and Spanish about bird flu risks; and continued support of states that are monitoring people with exposure to cows, birds, or other domestic and wild animals infected or potentially infected with avian influenza A(H5N1) viruses.
On August 9, 2024, CDC published an updated IRAT pandemic risk assessment for the A/Texas/37/2024 virus, linked to a human case of H5N1 bird flu in Texas related to dairy cows. Despite some risk factors changing slightly, the overall risk remains "moderate," similar to previous H5N1 clade 2.3.4.4b viruses. The IRAT assesses potential pandemic risks but does not predict pandemics or assess public risk, which remains low.
Colorado reported the first U.S. influenza A(H3N2) variant (v) virus infection in 2024 in a person who attended an agricultural event prior to becoming sick. When an influenza virus that normally spreads in pigs (swine) but not people is found in a person it is called a variant influenza virus. The person recovered without hospitalization. No additional cases or person-to-person spread have been identified. Since 2005, 517 variant influenza virus infections have been reported in the United States, generally linked to pig exposure.
