The CDC has released an updated evaluation of 11 novel flu subtypes/strains that currently circulate in non-human hosts, but that pose a potential threat to human health.
And if it seems as if the number of novel flu threats has increased markedly in recent years, you're right. Eight of the 11 viruses evaluated have emerged since 2011.
The CDC is quick to point out the Influenza Risk Assessment Tool (IRAT) is not predictive. As stated in their FAQ:
Can the IRAT predict a future pandemic?No. The IRAT is an evaluative tool, not a predictive tool. Flu is unpredictable, as are future pandemics.
But the IRAT can help planners decide which viruses pose the greatest risks, so they can prioritize their efforts and investments.
Of the 11 viruses evaluated:
- 5 are listed as having a moderate Potential Emergence Risk.
- 5 are listed as having a moderate Potential Impact Risk
- 1 (H7N9) is listed as having High-Moderate Potential Impact Risk
Follow the link to read the full report, including individual evaluations for each of the viruses in the table.
Summary of Influenza Risk Assessment Tool (IRAT) Results
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. Input is provided by U.S. government animal and human health influenza experts. Information about the IRAT is available at Influenza Risk Assessment Tool (IRAT) Questions and Answers .
Below is a table of results for influenza A viruses that have been assessed using IRAT because they serve as a representative of a particular subtype or are of unique interest.
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As we've seen repeatedly over the past few years, new subtypes can quickly emerge, and so this chart should not be considered a definitive list.
Since 2013 we've seen H7N9, H5N6, H10N8, H5N8, and H5N2 all emerge. Of these, H7N9 is viewed as posing the greatest risk of the lot.
Additional subtypes will almost certainly appear in the future. But for now, this evaluation tool can provide us with some relative risks for the subtypes currently circulating around the globe.