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.

Summary Results of Influenza A Viruses Assessed Using IRAT

Below is a table of results for influenza A viruses that have been assessed using IRAT because the viruses serve as a representative of a particular virus subtype or are of unique interest.
Influenza Virus Dates of Risk Assessment Potential Emergence Estimate Potential Impact Estimate Summary Risk Score Category
H1N1 [A/swine/Shandong/1207/2016] Jul 2020 7.5 6.9 Moderate
H1N1 [A/duck/New York/1996] Nov 2011 2.3 2.4 Low
H1N2 variant [A/California/62/2018] Jul 2019 5.8 5.7 Moderate
H3N2 variant [A/Ohio/13/2017] Jul 2019 6.6 5.8 Moderate
H3N2 variant [A/Indiana/08/2011] Dec 2012 6.0 4.5 Moderate
H3N2 [A/canine/Illinois/12191/2015] Jun 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 clade 2.3.4.4b [A/Astrakhan/3212/2020] Mar 2021 4.6 5.2 Moderate
H5N8 [A/gyrfalcon/Washington/41088/2014] Mar 2015 4.2 4.6 Low-Moderate
H7N7 [A/Netherlands/219/2003] Jun 2012 4.6  5.8 Moderate
H7N8 [A/turkey/Indiana/1573-2/2016] Jul 2017 3.4  3.9 Low
H7N9 [A/chicken/Tennessee/17-007431-3/2017] Oct 2017 3.1 3.5 Low
H7N9 [A/ chicken/Tennessee /17-007147-2/2017] Oct 2017 2.8 3.5 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
H9N2 Y280 lineage [A/Anhui-Lujiang/13/2018] Jul 2019 6.2 5.9 Moderate
H10N8 [A/Jiangxi-Donghu/346/2013] Feb 2014 4.3 6.0 Moderate

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IRAT Virus emergence and impact
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H1N1: Eurasian avian-like Swine Influenza A(H1N1) [A/swine/Shandong/1207/2016] Virus

Human infections with Eurasian avian-like swine influenza A(H1N1) viruses (EA SIV H1N1) have been reported occasionally in China. Some infected persons reported direct or indirect exposure to swine. While first reported in Europe in 1979, EA SIV H1N1 reached China as early as 1993. Multiple genotypes have since been identified in China as a result of reassortment with other SIVs. A recent paper by Sun et al. described six genotypes (designated G1-G6) of EA SIV H1N1 detected in China between 2011 and 2018, with 3 human infections in which the G4 genotype was detected. The G4 EA SIV H1N1 virus has been reported to show efficient infectivity and transmissibility in the ferret model and a study in China showed that antibody titers against G4 viruses were higher in swine workers compared to the general population, suggesting that additional human infections may have occurred. Full genome sequences of the G4 viruses indicated the presence of EA SIV H1N1 HA and NA genes with a unique combination of internal genes including A(H1N1)pdm09 virus PB2, PB1, PA, NP and M genes and a triple reassortant NS gene.

Summary:  A risk assessment of Eurasian avian-like swine influenza A(H1N1) [A/swine/Shandong/1207/2016] virus, clade 1C.2.3 and genotype 4, was conducted in July 2020. With point scores ranging from 1 to 10, the overall IRAT risk assessment score for this virus falls into the moderate risk category, which ranges from 4.0 to 7.9. The average risk score for potential emergence of the virus to achieve sustained human-to-human transmission was 7.5, within the upper moderate range. The average risk score for the virus to impact public health if it were to achieve sustained human-to-human transmission was 6.9, also in the upper moderate range. Full report here pdf icon[PDF – 272 KB].

H1N1: North American avian H1N1 [A/duck/New York/1996]

Avian influenza A viruses are designated as highly pathogenic avian influenza (HPAI) or low pathogenicity 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).

H1N2 variant: Swine Influenza A(H1N2) North American delta 2 lineage [A/California/62/2018] Virus

In July and August 2018, 13 human infections of influenza A(H1N2) variant virus were identified in the U.S. in three different states. In 11 of the infections, exposure to swine at an agricultural fair preceded the onset of illness and swine at the fairs were found infected with a closely related swine influenza A(H1N2) virus.  In one case, neither a connection to attendance at a fair nor exposure to swine was established, suggesting a possible person-to-person transmission event. Full genome sequence analysis of the viruses from these cases revealed all possessed hemagglutinin (HA) gene segments from the delta 2 sub-lineage of the North American swine A(H1) HA lineage.

Summary:  A risk assessment of swine influenza A(H1N2) North American delta 2 lineage A/California/62/2018 variant virus was conducted in July 2019. The overall IRAT risk assessment score for this virus falls into the moderate risk category. The summary average risk score for the virus to achieve sustained human-to-human transmission was 5.8.  The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was 5.7, also in the moderate range. For a full report click here pdf icon[282 KB, 4 pages].

H3N2 variant: Swine Influenza A(H3N2) North American 2010.1 lineage [A/Ohio/13/2017] Virus

In July and August 2016, 18 human infections of influenza A(H3N2) variant [A(H3N2)v] virus were identified in the U.S. in two different states. All 18 infections involved exposure to swine at agricultural fairs prior to onset of illness and swine at these fairs were found infected with swine influenza A(H3N2) virus. Full genome sequence analysis of the viruses from these cases revealed that all possessed a human-like hemagglutinin (HA) likely derived from seasonal human A(H3N2) influenza virus from 2010. In 2017, sixty-two human infections with influenza A(H3N2)v virus were reported from nine different states and were closely related to the viruses detected in human infections in 2016.

Summary:  A risk assessment of swine influenza A(H3N2) North American 2010.1 lineage A/Ohio/13/2017 variant virus was conducted in July 2019. The overall IRAT risk assessment score for this virus falls into the moderate risk category. The summary average risk score for the virus to achieve sustained human-to-human transmission was 6.6.  The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was 5.8, also in the moderate range. For a full report click here pdf icon[328 KB, 6 pages].

H3N2 variant: [A/Indiana/08/11]

Swine-origin influenza 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 a hemagglutinin gene belonging to cluster IV of swine influenza viruses and 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 influenza 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). For a full report click here pdf icon[186 KB, 4 pages].

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, HPAI H5N1 viruses have caused over 860 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 was a reassortant 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 a similar virus from a backyard flock in the Fraser Valley. When this risk assessment was conducted in 2015, these were the only reported detections of this specific 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 reassortant 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 May 2019, there have been 23 human cases of H5N6 highly pathogenic avian influenza reported and 14 of the cases were fatal. Avian outbreaks of this virus were first reported from China in 2013. Subsequently, avian outbreaks have been reported in several countries through 2019.

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: Highly Pathogenic Avian Influenza A(H5N8) clade 2.3.4.4b [A/Astrakhan/3212/2020]

The first human infection with genetic clade 2.3.4.4b A(H5N8) highly pathogenic avian influenza viruses (AIV), was reported in the Russian Federation in February 2021. Of the seven persons detected with A(H5) virus, one infection was confirmed with AIV A(H5N8) clade 2.3.4.4b, and all had reported exposure to layer hens infected with the same subtype and clade during a poultry farm outbreak in December 2020. All A(H5N8) human cases remained asymptomatic. Avian influenza A(H5) viruses of the A/goose/Guangdong/1/96-lineage have spread from Asia to Europe through wild birds since 2004. Clade 2.3.4.4 A(H5) viruses have reassorted with other AIVs, resulting in multiple A(H5) virus subtypes and genotypes detected in Asia, the Middle East, Europe, and Africa. AIV A(H5N8) clade 2.3.4.4 was identified in the Russian Federation for the first time in 2014, with clade 2.3.4.4b detected in wild birds as early as 2017. Analyses indicate that AIV A(H5N8) clade 2.3.4.4b has maintained the characteristics typical of viruses adapted to avian species. The hemagglutinin of A/Astrakhan/3212/2020 differed by no more than 3 amino acids from the A(H5N6) A/Fujian-Sanyuan/21099/2017 candidate vaccine virus and the majority of viruses detected in birds in the Russian Federation during 2016, 2017, and 2018.These poultry viruses reacted well with post-infection ferret antisera raised against the A/Fujian- Sanyuan/21099/2017 candidate vaccine virus.

Summary: A risk assessment of clade 2.3.4.4b, highly pathogenic avian influenza A(H5N8) virus, and the representative virus, A/Astrakhan/3212/2020, was conducted in March 2021. The overall estimated IRAT scores placed this virus in the lower to middle range of the moderate risk category, (which ranges from 4.0 to 7.9). The average risk score for the estimated potential emergence of the virus to achieve sustained human-to-human transmission was 4.6, in the lower range of the moderate risk category. The average risk score for the virus to potentially impact public health if it were to achieve sustained human- to-human transmission was 5.2, in the lower to middle range of the moderate risk category. The average confidence level in the available data of all 10 risk elements was 2.1 (range: 1.0,3.2). Full report pdf icon[PDF – 350 KB].

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 detected in 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 detected 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).

H7N7: [A/Netherlands/219/03]

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) H7N8 virus of North American lineage was identified in a commercial turkey flock in Indiana. Subsequent investigation of the affected farm and surrounding farms revealed no additional HPAI viruses, but low pathogenicity avian influenza (LPAI) viruses with highly similar genomes to the HPAI virus were detected in 9 other turkey flocks in the area. There were no reports of human cases associated with these viruses. A representative LPAI virus from the outbreak, A/turkey/Indiana/1573-2/2016, was assessed using IRAT.

Summary: A risk assessment of LPAI virus, A/turkey/Indiana/1573-2/2016, 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).

H7N9: Asian avian [A/Hong Kong/125/2017]

Low pathogenicity avian influenza (LPAI) H7N9 viruses were first reported from China in March 2013. These viruses were first scored using the IRAT in April 2013, and then annually in 2014, 2015, and 2016 with no change in overall risk scores. Between October 2016 and May 2017, two divergent lineages of these viruses were 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). For a full report, click here pdf icon[262 KB, 4 pages].

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 May 2019, the WHO has received reports of 1,568 cases, 615 have died. This low pathogenicity 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).

H7N9: Low Pathogenicity North American avian [A/chicken/Tennessee/17-007431-3/2017]

Surveillance conducted in March 2017 during the investigation of a highly pathogenic avian influenza (HPAI) A(H7N9) virus in commercial poultry in Tennessee revealed the contemporaneous presence of North American lineage low pathogenicity avian influenza (LPAI) A(H7N9) virus in commercial and backyard poultry flocks in Tennessee and three other states. The outbreak in poultry appeared limited with no further detections in subsequent surveillance. There were no reports of human cases associated with this virus.

Summary:  A risk assessment of this North American lineage LPAI A(H7N9) virus was conducted in October 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 was in the low risk category (score 3.1).  The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was between the low to low-moderate range (score 3.5). For a full report, click here pdf icon[228 KB, 4 pages].

H7N9: Highly Pathogenic North American avian [A/chicken/Tennessee/17-007147-2/2017]

In March 2017, the U.S. Department of Agriculture (USDA) reported the detection of a highly pathogenic avian influenza (HPAI) A(H7N9) virus in 2 commercial poultry flocks in Tennessee. Full genome sequence analysis indicated that all eight gene segments of the virus were of North American wild bird lineage and genetically distinct from the lineage of influenza A(H7N9) viruses infecting poultry and humans in China since 2013. The outbreak investigation revealed that a related North American low pathogenicity avian influenza A(H7N9) was circulating in poultry prior to the detection of the HPAI A(H7N9). There were no reports of human cases associated with this virus.

Summary:  A risk assessment this North American lineage HPAI A(H7N9) virus was conducted in October 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 (2.8). 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 (3.5). For a full report, click here pdf icon[225 KB, 4 pages].

H9N2: Avian H9N2 G1 lineage [A/Bangladesh/0994/2011]

Human infections with influenza A(H9N2) virus have been reported sporadically, cases reportedly exhibited mild influenza-like illness. Historically, these low pathogenicity 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).

H9N2: Avian Influenza A(H9N2) Y280 lineage [A/Anhui-Lujiang/39/2018] Virus

Low pathogenic avian influenza A(H9N2) viruses are enzootic in poultry in many countries in Africa, Asia, the Middle East, and Europe. Since the late 1990s when the first human infections with avian influenza A(H9N2) virus were identified, detection of this virus has been reported infrequently in humans and in swine and other mammals. In 2018, there were 7 reported human infections, most with known exposure to poultry and with the majority involving viruses of the Y280 lineage.

Summary:  A risk assessment of avian influenza A(H9N2) Y280 lineage A/Anhui-Lujiang/39/2018 virus was conducted in July 2019. The overall IRAT risk assessment score for this virus falls into the moderate risk category. The summary average risk score for the virus to achieve sustained human-to-human transmission was 6.2. The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was 5.9, also in the moderate range. For a full report click here pdf icon[356 KB, 5 pages].

H10N8: Avian H10N8 [A/Jiangxi-Donghu/346/2013]

Three human infections with influenza A(H10N8) virus were reported by the China Health and Family Planning Commission in 2013 and 2014. All cases were hospitalized and two died. Historically, low pathogenicity 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).

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