#18,234
Late this afternoon the CDC released the results of their promised IRAT (Influenza Risk Assessment Tool) assessment of the recently emerged A/Texas/37/2024 H5N1 virus, which has affected dairy cattle, poultry, humans and spilled over into a number of other mammals across the United States over the past 6 months or so.
This is the first addition to the IRAT list since the Risk Assessment On Mink Variant of Avian H5N1, which was published in July of 2023. Today's addition is the 10th H5 virus to make the list, and the 25th novel virus overall.
The CDC described the release in today's CDC A(H5N1) Bird Flu Response Update August 9, 2024, which also notes that the cutoff date on this assessment was in late June, prior to the recent spate of human cases reported in Colorado (see below).
A new CDC report published today summarizes the findings of an assessment of the potential pandemic risk associated with an avian influenza A(H5N1) virus (clade 2.3.4.4b [A/Texas/37/2024]) isolated from a human case in Texas. The assessment was performed using the Influenza Risk Assessment Tool, an instrument developed by CDC and external influenza experts to evaluate the pandemic potential of influenza A viruses that currently circulate in animals but not in humans. The future pandemic potential of a virus is different from the immediate population or individual health risk, which is unchanged and remains low. Findings of IRATs are used to inform preparedness planning. This most recent IRAT score validates the proactive, coordinated U.S. government response. Systematic comparisons of data related to this avian influenza A(H5N1) virus using the IRAT to data from other influenza A viruses has scored this virus's future pandemic potential as "moderate" based on information through June 26, 2024. This is similar to previous assessments of earlier avian influenza A(H5N1) viruses.
This analysis, which includes data through June 26, 2024, did not include the 10 human infections that occurred in Colorado in July following exposure to infected poultry (9 cases) and dairy cows (1 case). All were associated with mild illness and a majority experienced conjunctivitis. CDC completed the report to inform ongoing preparedness efforts.
This IRAT seeks to compare this `bovine' strain to the Spanish `Mink Strain' added last year, and a strain collected in 2022 in South Carolina from a Wigeon. Today's CDC weekly update summarized the findings:
This IRAT assessment indicates that while the virus that caused an H5N1 bird flu infection in a person in Texas [A/Texas/37/2024 virus] in 2024 scored slightly lower in some risk elements and slightly higher in others compared with two previously assessed avian influenza A(H5N1) clade 2.3.4.4b viruses, the mean-high and mean-low acceptable score ranges for these viruses overlap. This means that the future pandemic potential risk from these viruses remains similar and is classified as "moderate" risk.
Their assessment puts A/Texas/37/2024 8th from the top, in terms of risk, with China's Swine-variant EA H1N1 `G4' virus - which we've been following since 2015 - still firmly at the top of the list.
The Key Findings from the report - and a link to the full PDF - follow:
On August 9, 2024, CDC published a new IRAT assessment for A/Texas/37/2024, an avian influenza A(H5N1) clade 2.3.4.4b virus that was associated with a human infection in a person in Texas who had exposure to A(H5N1) virus-infected dairy cows. Avian influenza A(H5N1) clade 2.3.4.4b viruses are causing outbreaks in wild birds and poultry, occasional infections in mammals, and rare human infections in the United States and globally. Between April 1, 2024 and August 9, 2024, eight human cases of A(H5N1) bird flu and five human cases of A(H5) bird flu were reported in the United States. The first of these was reported on April 1, 2024, when theA/Texas/37/2024 State of Texas announced that a person tested positive for HPAI A(H5N1) virus.
Previously, CDC had assessed two other avian influenza A(H5N1) clade 2.3.4.4b viruses: the A/American wigeon/South Carolina/AH0195145/2021 and the A/mink/Spain/3691-8_22VIR10586-10/2022. Both viruses had overall estimated IRAT scores in the moderate risk category range of 4.0 to 7.9.
This updated assessment includes new information since then, including information from additional human cases reported in the United States (but excluding recent human cases among poultry workers associated with exposure to infected poultry at poultry farms in Colorado). This updated assessment using the virus from the first human case in Texas, indicates that this A/Texas/37/2024 virus has scored slightly lower in some risk elements and slightly higher in others compared with the previously assessed H5N1 clade 2.3.4.4b viruses. However, the mean-high and mean-low acceptable score ranges for these viruses overlap, indicating that these viruses remain similar, and their overall risk scores remain "moderate." New data visualizations have been added to this page to aid in the comparison of these viruses.
The Influenza Risk Assessment Tool (IRAT) is an evaluation tool conceived by CDC and further developed with assistance from global animal and human health influenza experts. The IRAT is used to assess the potential pandemic risk posed by influenza A viruses that are not currently circulating in people. The IRAT does not predict pandemics, and the IRAT is not used to assess the risk of H5N1 bird flu to the general public, which current remains low. Input on IRAT assessments is provided by a diverse group of U.S. government animal and human health influenza experts. More information about the IRAT, including a description of its methodology and definitions for its risk elements and categories, is available at Influenza Risk Assessment Tool (IRAT). The IRAT is updated when new zoonotic or novel influenza viruses with pandemic potential emerge or undergo a change in characteristics that prompts the need for a new assessment.
The full report is available.
Follow this link to read the full summary.
