Influenza Risk Assessment Tool (IRAT) Virus Descriptions and Report Summaries

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).

Flu Date: Nov 1, 2011

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 [272 KB].

Flu Date: Jul 1, 2020

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. Full report [282 KB, 4 pages]. in the moderate risk range (less than 7).

Flu Date: Jul 1, 2019

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. Full report [328 KB, 6 pages].eve sustained human-to-human transmission was in the moderate risk range (less than 7).

Flu Date: Jul 1, 2019

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). Full report [186 KB, 4 pages].

Flu Date: Jun 1, 2016

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).ve sustained human-to-human transmission was in the moderate risk range (less than 7).

Flu Date: Dec 1, 2012

Purpose: The current overall individual and population health risk to the general public posed by the avian influenza A(H5N1) virus presently spreading in cows, poultry, and other mammals remains low. Systematic comparisons of data related to this avian influenza A(H5N1) virus using the Influenza Risk Assessment Tool (IRAT) to data from other influenza A viruses has scored this virus's future pandemic potential as "moderate risk" based on information through June 26, 2024. This is similar to previous assessments of earlier avian influenza A(H5N1) viruses.

The IRAT uses expert opinion to evaluate the potential of a representative novel influenza virus to gain the ability for person-to-person spread and the resulting potential public health impact if that were to happen, compared to other viruses evaluated in past IRAT reports. The IRAT does not assess the immediate risk to the public's health, which is unchanged and remains low, and it does not predict future pandemics.

This report summarizes the findings of an IRAT conducted on a recent avian influenza A(H5N1) virus from a human case in Texas (A/Texas/37/2024). The score places the currently circulating avian influenza A(H5N1) virus in the category of "moderate risk" for potential future emergence and public health impact. This is similar to previous assessments of earlier avian influenza A(H5N1) viruses. The scores for this IRAT were submitted June 26, 2024, prior to additional human cases in Colorado. The report was completed expeditiously based on data as of June 26 to inform ongoing preparedness discussions.

During a public health response, the IRAT can be used to assess the appropriateness of the ongoing response efforts and whether additional actions are warranted based on the risk score. The results of this IRAT validate the proactive, coordinated U.S. government response. Assessing risk is an iterative process with new information being assimilated regularly and response activities adjusted as indicated.

Key findings: Since January 2022, highly pathogenic avian influenza (HPAI) A(H5N1) virus clade 2.3.4.4b has been detected in the United States in numerous wild bird species, including aquatic birds such as ducks, and in commercial and backyard domestic poultry in most states.

The A(H5N1) clade 2.3.4.4b virus emerged in 2020, spreading across Europe, Asia, and Africa, in both wild aquatic birds and domestic poultry, and by 2021, replaced the previously circulating A(H5N8) clade 2.3.4.4b viruses. This virus was first reported in migrating wild aquatic birds in North America in December 2021 and in South America in January 2023. In 2023, the virus was detected in around 70 countries. The first detections in the United States were from migratory wild aquatic birds but the virus has also been detected in domestic poultry. Sporadic incursions of the virus into aquatic and terrestrial carnivorous mammals have occurred in the United States and other regions, including an outbreak in a farmed mink unit in Spain and elephant seals in Argentina.

From January 2022 through July 17, 2024, thirty-seven cases of influenza A(H5N1) virus infection in humans have been reported globally. Of those with available sequence data, nineteen of these cases were identified with A(H5N1) clade 2.3.4.4b viruses. Four of these cases resulted in severe/critical lower respiratory tract disease with one fatality.

In the United States, during January 2022 through July 17, 2024, there have been five cases of A(H5N1), and five cases of A(H5) reported in humans. One human case of A(H5N1) was reported in the United States in April 2022 in a farm worker who experienced fatigue without any other symptoms while depopulating poultry at a poultry farm with confirmed A(H5N1). However, it is possible that this case did not represent a true infection, but rather detection of a low level of A(H5N1) viral RNA in a respiratory specimen due to environmental contamination. Environmental contamination was previously attributed to two asymptomatic cases in poultry workers reported in Spain.

Since April 2024, four human cases of A(H5N1) and five cases of A(H5) have been reported in the United States. Three A(H5N1) cases and one A(H5) case have been associated with an ongoing multi-state outbreak of A(H5N1) in dairy cattle: on April 1st, the State of Texas announced that a person tested positive for A(H5N1), in May, Michigan announced detection of two A(H5N1) cases occurring at different farms, and on July 3rd, Colorado announced a human case of A(H5). All of these cases have been associated with an ongoing multi-state outbreak of A(H5N1) in dairy cattle. Additionally, all infections occurred in dairy workers who had direct exposure to cattle presumed to be infected with A(H5N1) virus. All patients reported eye redness/watery eyes, and one patient also had cough without fever. No patients have been hospitalized.

One additional A(H5N1) case and four cases of A(H5) were recently identified in Colorado. All of these cases were in farm workers who were involved in the depopulation of poultry at a poultry facility experiencing an outbreak of HPAI A(H5N1) virus. These workers reported symptoms after being exposed to A(H5N1) virus-infected poultry. All workers who tested positive reported mild illness. The workers reported redness/watery eyes and respiratory symptoms

Phylogenetic analysis of A(H5N1) clade 2.3.4.4b viruses shows high levels of genetic similarity to previously circulating A(H5Nx) clade 2.3.4.4b viruses, with little evidence of mammalian adaptation. The hemagglutinin (HA) genes of currently circulating wild bird and poultry A(H5N1) clade 2.3.4.4b viruses show a high level of genetic similarity to previous clade 2.3.4.4 viruses, with some genetic variation noted among the N1 neuraminidase (NA) gene, which is wild bird adapted.

Previously recommended A(H5) candidate vaccine viruses (CVVs) are expected to be effective against A(H5N1) viruses currently circulating among wild birds, poultry, and cattle. In addition, A(H5N1) virus genetic analysis suggests that a majority of viruses remain susceptible to available FDA-approved influenza antiviral medications.

Using the IRAT, the Centers for Disease Control and Prevention (CDC) assessed the pandemic potential of HA clade 2.3.4.4b, AIV A(H5N1) viruses using A/Texas/37/2024 as the prototype strain. Previously, CDC has assessed two other HPAI 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.

Summary: This updated assessment 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." The moderate risk category, ranges from 4.0 to 7.9. The average risk score for the estimated potential emergence of the virus was 5.79, in the mid-low range of the moderate risk category. The average risk score for the virus to potentially impact public health was 6.12, in the mid-range of the moderate risk category. These scores reflect an increase of 0.66 in the emergence question and a decrease of 0.12 in the impact question compared to the previous A(H5N1) evaluation last year, but both questions still fall into the moderate risk category. The average SME confidence level in the available data of all 10 risk elements was 2.26 (SME confidence range: 0.00-4.00).

The estimates for this A(H5N1) clade 2.3.4.4b virus were in the mid-moderate range for both risk of potential emergence and risk of potential public health impact. The average score estimates ranked this virus sixth highest risk for the emergence and seventh highest risk for the impact risks when compared to the other 15 viruses scored with the IRAT to date.

A bar graph comparing each of the 10 weighted average risk elements scores for A/Texas, the mink, and American wigeon virus is available: Summary of Influenza Risk Assessment Tool (IRAT) Results. The full report is available.

Flu Date: August 9, 2024

Since January 2022, highly pathogenic avian influenza A(H5N1) virus (AIV) clade 2.3.4.4b has been detected in the United States in numerous wild bird species, including aquatic birds such as ducks, and in commercial and backyard domestic poultry in multiple states.

The A(H5N1) clade 2.3.4.4b virus emerged in 2020, spreading across Europe, Asia, and Africa, in both wild aquatic birds and domestic poultry, and replacing the previously circulating A(H5N8) clade 2.3.4.4b viruses by 2021. This virus was first reported in migrating wild aquatic birds in North America in December 2021 and in South America in January 2023. In 2023, the virus has been detected in more than 50 countries in these five regions. The first detections in the United States were from migratory wild aquatic birds but the virus has also been detected in domestic poultry. Sporadic incursions of the virus into aquatic and terrestrial carnivorous mammals have occurred in the United States and other regions, including an outbreak in a farmed mink unit in Spain.

Between 2022-2023, nine cases of human infection with A(H5N1) clade 2.3.4.4b viruses have been identified in Europe, Asia, and the Americas. Five of these cases resulted in severe/critical lower respiratory tract disease with one fatality.

Phylogenetic analysis of A(H5N1) clade 2.3.4.4b viruses shows high levels of genetic similarity to previously circulating A(H5Nx) clade 2.3.4.4b viruses, with little evidence of mammalian adaptation. The hemagglutinin (HA) genes of currently circulating wild bird and poultry A(H5N1) clade 2.3.4.4b viruses show a high level of genetic similarity to previous clade 2.3.4.4 viruses, with some genetic variation noted among the N1 neuraminidase (NA) gene, which is wild bird adapted.

Previously recommended A(H5) candidate vaccine viruses (CVVs) are expected to be effective against A(H5N1) viruses currently circulating among wild birds and poultry. In addition, A(H5N1) virus genetic analysis suggests that a majority of viruses remain susceptible to available influenza antiviral medications.

Summary: A re-evaluation of the risk assessment of highly pathogenic avian influenza A(H5N1) virus clade 2.3.4.4b, using A/mink/Spain/3691-8_22VIR10586-10/2022 as the new prototype strain, was conducted in April 2023. The overall estimated IRAT scores placed this virus in the moderate risk category, which ranges from 4.0 to 7.9. The average risk score for the estimated potential emergence of the virus was 5.13, in the mid-low range of the moderate risk category. The average risk score for the virus to potentially impact public health was 6.24, in the mid-range of the moderate risk category. These scores reflect an increase of 0.69 in the emergence question and an increase of 1.17 in the impact question compared to the previous A(H5N1) evaluation last year, but both questions still fall into the moderate risk category.

The mink virus scores higher than the previously assessed American wigeon virus across 6 out of the 10 risk elements evaluated by the IRAT, including the following: antiviral treatment options, disease severity and pathogenesis, genomic analysis, human infections, infections in animals, and transmission in animal models. These increased scores reflect new information about HPAI H5 2.3.4.4b viruses, including seven new human detections–many with severe clinical courses. Additionally, there have been sporadic infections and sustained transmission in wild birds and domestic poultry in Asia, Europe, Africa, and the Americas, including multiple detections in mammals with genetic markers of importance for mammalian/human infection (but not in birds). A bar graph comparing each of the 10 weighted average risk elements scores for the mink and American wigeon virus is available Summary of Influenza Risk Assessment Tool (IRAT) Results. The average subject matter expert (SME) confidence level in the available data of all 10 risk elements was 2.32 (SME confidence range: 1.0-4.0). The full report [486 KB, 8 Pages] is available.

Flu Date: Apr 1, 2023

Since January 2022, highly pathogenic avian influenza A(H5N1) virus clade 2.3.4.4b has been detected in the United States in numerous wild bird species, including aquatic birds such as ducks, and in commercial and backyard domestic poultry in numerous states.

The A(H5N1) clade 2.3.4.4b virus emerged in 2020, spreading across Europe, Asia, and Africa, in both wild aquatic birds and domestic poultry, and replacing the previously circulating A(H5N8) clade 2.3.4.4b viruses by 2021. In 2022, the virus has been detected in more than 50 countries in these three regions and was first reported in migrating wild aquatic birds in the Americas in December 2021. First detections in the United States also were from migratory wild aquatic birds.

In January 2022, one asymptomatic human infection with this virus, with known repeated exposure to infected ducks in England, was reported to the World Health Organization.

Phylogenetic analysis of A(H5N1) clade 2.3.4.4b viruses show high levels of genetic similarity to previously circulating A(H5Nx) clade 2.3.4.4b viruses, with little to no evidence of mammalian adaptation. The hemagglutinin genes of circulating wild bird and poultry viruses show a high level of genetic similarity, with some genetic variability noted among the neuraminidase gene, which is wild bird adapted.

Previously recommended A(H5) candidate vaccine viruses are expected to be effective against A(H5N1) viruses currently circulating among wild birds and poultry. In addition, A(H5N1) virus genetic and phenotypic analysis suggests that they remain susceptible to available influenza antiviral medications.

Summary: A risk assessment of highly pathogenic avian influenza A(H5N1) virus clade 2.3.4.4b, using A/American wigeon/South Carolina/AH0195145/2021 as the prototype strain, was conducted in March 2022. The overall estimated IRAT scores placed this virus in the moderate risk category, which ranges from 4.0 to 7.9. The average risk score for the estimated potential emergence of the virus was 4.4, in the lower range of the moderate risk category. The average risk score for the virus to potentially impact public health was 5.1, also in the lower range of the moderate risk category. The average confidence level in the available data of all 10 risk elements was 2.4 (range: 1.0-3.0). For full report see Full report [462 KB, 6 pages].

Flu Date: Mar 1, 2022

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).

Flu Date: Mar 1, 2015

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).

Flu Date: Nov 1, 2011

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).

Flu Date: Mar 1, 2015

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).ve sustained human-to-human transmission was in the moderate risk range (less than 7).

Flu Date: Mar 1, 2021

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 [350 KB].

Flu Date: Mar 1, 2021

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).

Flu Date: Mar 1, 2015

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).

Flu Date: Jun 1, 2012

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).

Flu Date: Jul 1, 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). Full report [262 KB, 4 pages].

Flu Date: May 1, 2017

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).

Flu Date: Apr 1, 2016

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). Full report [228 KB, 4 pages].

Flu Date: Oct 1, 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). Full report [225 KB, 4 pages].

Flu Date: Oct 1, 2017

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. Full report [356 KB, 5 pages].

Flu Date: Jul 1, 2019

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).

Flu Date: Feb 1, 2014

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).

Flu Date: Feb 1, 2014