Summary of Influenza Risk Assessment Tool (IRAT) Results
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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.
| Virus | Most Recent Date Evaluated | Potential Emergence Risk | Potential Impact Risk | Overall Summary |
|---|---|---|---|---|
| H1N1 [A/duck/New York/1996] | Nov 2011 | 2.3 | 2.4 | Low |
| H3N2 variant [A/Indiana/08/2011] | Dec 2012 | 6.0 | 4.5 | Moderate |
| H3N2 [A/canine/Illinois/12191/2015] | June 2016 | 3.7 | 3.7 | Low |
| H5N1 Clade 1 [A/Vietnam/1203/2004] | Nov 2011 | 5.2 | 6.6 | Moderate |
| H5N1 [A/American green-winged teal/Washington/1957050/2014] | Mar 2015 | 3.6 | 4.1 | Low-Moderate |
| H5N2 [A/Northern pintail/Washington/40964/2014] | Mar 2015 | 3.8 | 4.1 | Low-Moderate |
| H5N6 [A/Yunnan/14564/2015] – like | Apr 2016 | 5.0 | 6.6 | Moderate |
| H5N8 [A/gyrfalcon/Washington/41088/2014] | Mar 2015 | 4.2 | 4.6 | Low-Moderate |
| H7N7 [A/Netherlands/2019/2003] | Jun 2012 | 4.6 | 5.8 | Moderate |
| H7N8 [A/turkey/Indiana/1573-2/2016] | July 2017 | 3.4 | 3.9 | Low |
| H7N9 [A/Hong Kong/125/2017] | May 2017 | 6.5 | 7.5 | Moderate-High |
| H7N9 [A/Shanghai/02/2013] | Apr 2016 | 6.4 | 7.2 | Moderate-High |
| H9N2 G1 lineage [A/Bangladesh/0994/2011] | Feb 2014 | 5.6 | 5.4 | Moderate |
| H10N8 [A/Jiangxi-Donghu/346/2013] | Feb 2014 | 4.3 | 6.0 | Moderate |
H1N1: [North American avian H1N1 [A/duck/New York/1996]
Avian influenza A viruses are designated as highly pathogenic avian influenza (HPAI) or low pathogenic avian influenza (LPAI) based on molecular characteristics of the virus and the ability of the virus to cause disease and death in chickens in a laboratory setting. North American avian H1N1 [A/duck/New York/1996] is a LPAI virus and in the context of the IRAT serves as an example of a low risk virus.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the low risk category (less than 3). Similarly the average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission also falls into the low risk range (less than 3).
H3N2 Variant:[A/Indiana/08/11]
Swine-origin flu viruses do not normally infect humans. However, sporadic human infections with swine-origin influenza viruses have occurred. When this happens, these viruses are called “variant viruses.” Influenza A H3N2 variant viruses (also known as “H3N2v” viruses) with the matrix (M) gene from the 2009 H1N1 pandemic virus were first detected in people in July 2011. The viruses were first identified in U.S. pigs in 2010. In 2011, 12 cases of H3N2v infection were detected in the United States. In 2012, 309 cases of H3N2v infection across 12 states were detected. The latest risk assessment for this virus was conducted in December 2012 and incorporated data regarding population immunity that was lacking a year earlier.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the moderate risk category (less than 6). The summary average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the low-moderate risk category (less than 5).
H3N2: [A/canine/Illinois/12191/2015]
The H3N2 canine influenza virus is an avian flu virus that adapted to infect dogs. This virus is different from human seasonal H3N2 viruses. Canine influenza A H3N2 virus was first detected in dogs in South Korea in 2007 and has since been reported in China and Thailand. It was first detected in dogs in the United States in April 2015. H3N2 canine influenza has reportedly infected some cats as well as dogs. There have been no reports of human cases.
Summary: The average summary risk score for the virus to achieve sustained human-to-human transmission was low risk (less than 4). The average summary risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the low risk range (less than 4).
H5N1 clade 1: [A/Vietnam/1203/2004]
The first human cases of highly pathogenic avian influenza (HPAI) H5N1 virus were reported from Hong Kong in 1997. Since 2003, highly pathogenic H5N1 avian influenza viruses have caused over 850 laboratory-confirmed human cases; mortality among these cases was high. A risk assessment of this H5N1 clade 1 virus was conducted in 2011 soon after the IRAT was first developed and when 12 hemagglutinin (HA) clades were officially recognized.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the moderate risk category (less than 6). The summary average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the high-moderate risk category (less than 7).
H5N1: [A/American green winged teal/Washington/1957050/2014]
In December 2014, an H5N1 highly pathogenic avian influenza virus was first isolated from an American green-winged teal in the state of Washington. This virus is a recombinant virus containing four genes of Eurasian lineage (PB2, HA, NP and M) and four genes of North American lineage (PB1, PA, NA and NS).In February 2015, the Canadian government reported isolating this virus from a backyard flock in the Fraser Valley. When this risk assessment was conducted in 2015, these were the only reported isolations of this virus. There have been no reports of human cases.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the low risk category (less than 4). The summary average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the low-moderate risk category (less than 5).
H5N2: [A/Northern pintail/Washington/40964/2014]
In December 2014, an H5N2 highly pathogenic avian influenza virus was first reported by the Canadian government from commercial poultry in the Fraser Valley.Subsequently this virus was isolated from wild birds, captive wild birds, backyard flocks and commercial flocks in the United States.This virus is a recombinant virus composed of five Eurasian lineage (PB2, PA, HA, M and NS) genes and three North American lineage (PB1, NP and NA) genes. There have been no reports of human cases.
Summary: The average summary risk score for the virus to achieve sustained human-to-human transmission was low risk (less than 4).The average summary risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the low-moderate risk range (less than 5).
H5N6: [A/Yunnan/14564/2015 (H5N6-like)]
Between January 2014 and March 2016, there have been 10 human cases of H5N6 highly pathogenic avian influenza reported. Nine reportedly experienced severe disease and six died. Avian outbreaks of this virus were first reported from China in 2013. Subsequently avian outbreaks have been reported in at least three countries (China, Vietnam and Lao PDR) through 2015.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the moderate range (less than 6).The average summary risk score for the virus to significantly impact on public health if it were to achieve sustained human-to-human transmission fell in the moderate range (less than 7).
H5N8: [A/gyrfalcon/Washington/41088/2014]
In December 2014, an H5N8 highly pathogenic avian influenza virus was first isolated from a sample collected in the United States from a captive gyrfalcon.Subsequently this virus was isolated from wild birds, captive wild birds, backyard flocks and commercial flocks in the United States.This virus (clade 2.3.4.4) is similar to Eurasian lineage H5N8 viruses that have been isolated in South Korea, China, Japan, the Netherlands, the United Kingdom and Germany in late 2014-early 2015.There have been no reports of human cases.
Summary: The average risk score for the virus to achieve sustained human-to-human transmission was in the low-moderate range< (less than 5). The average summary risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission fell in the low-moderate range (less than 5).
In 2003 the Netherlands reported highly pathogenic avian influenza (HPAI) in approximately 255 commercial flocks.Coinciding with human activities around these infected flocks, 89 human cases of H7N7 were identified.Cases primarily reported conjunctivitis, although a few also reported mild influenza-like illness.There was one death.
Summary: The summary average risk score for this virus to achieve sustained human-to-human transmission was in the low-moderate risk range (less than 5). The summary average risk score for this virus to significantly impact the public’s health if it were to achieve sustained human-to-human transmission fell in the moderate risk range (less than 7).
H7N8: [A/turkey/Indiana/1573-2/2016]
In January 2016, a highly pathogenic avian influenza (HPAI) virus of North American lineage was identified in a turkey flock in Indiana. Putative low pathogenic avian influenza (LPAI) viruses similar to A/turkey/Indiana/1573-2/2016 were subsequently isolated from 9 other turkey flocks in the area. There were no reports of human cases associated with this virus at the time of the IRAT scoring.
Summary: A risk assessment of this LPAI virus was conducted in July 2017. The overall IRAT risk assessment score for this virus falls into the low risk category (< 4). The summary average risk score for the virus to achieve sustained human-to-human transmission is in the low risk category (3.4). The summary average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was also in the low risk category (3.9).
Low pathogenic avian influenza (LPAI) H7N9 viruses were first reported from China in March 2013. These viruses were first scored using the IRAT in March 2013 and again in April 2013, and then annually in 2014, 2015, and 2016 with no change in overall risk scores. Between October 2016 and May 2017 evidence of two divergent lineages of these viruses was detected – the Pearl River Delta lineage and the Yangtze River Delta lineage. The IRAT was used to assess LPAI H7N9 [A/Hong Kong/125/2017], a representative of the Yangtze River Delta viruses.
Summary: A risk assessment of H7N9 [A/Hong Kong/125/2017] was conducted in May 2017. The overall IRAT risk assessment score for this virus falls into the moderate-high risk category and is similar to the scores for the previous H7N9 viruses. The summary average risk score for the virus to achieve sustained human-to-human transmission is in the moderate risk category (less than 7). The summary average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the moderate-high risk category (less than 8).
H7N9: Avian H7N9 [A/Shanghai/02/2013]
On 31 March 2013, the China Health and Family Planning Commission notified the World Health Organization (WHO) of three cases of human infection with influenza H7N9. As of August 2016, the WHO has received reports of 821 cases, 305 have died. This low pathogenic avian influenza virus was rescored most recently in April 2016 with no substantive change in risk scores since May 2013.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the moderate risk category (less than 7). The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission fell in the high-moderate risk range (less than 8).
H9N2: Avian H9N2 G1 lineage [A/Bangladesh/0994/2011]
Human infections with influenza AH9N2 virus have been reported sporadically, cases reportedly exhibited mild influenza-like illness. Historically these low pathogenic avian influenza viruses have been isolated from wild and domestic birds. In response to these reports, a risk assessment of this H9N2 influenza virus was conducted in 2014.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was in the moderate risk category (less than 6). The summary average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission also fell in the moderate risk range (less than 6).
H10N8: Avian H10N8 [A/Jiangxi-Donghu/346/2013]
Two human infections with influenza A(H10N8) virus were reported by the China Health and Family Planning Commission in 2013 and 2014 (one each year). Both cases were hospitalized and one died. Historically low pathogenic avian influenza H10 and N8 viruses have been recovered from birds. A risk assessment of the H10N8 influenza was conducted in 2014.
Summary: The summary average risk score for the virus to achieve sustained human-to-human transmission was low-moderate (less than 5). The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the moderate risk range (less than 7).
- Page last reviewed: August 2, 2017
- Page last updated: August 2, 2017
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- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
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