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Five years ago, in CDC: IRAT Evaluation Of Novel Avian & Swine Flu Risks, we looked at the CDC's assessment tool which ranked the 11 most worrisome novel flu subtypes/strains that circulated in non-human hosts, and that posed a potential threat to human health.
Of particular note, 8 of those 11 viruses had emerged since 2011, highlighting the rapid evolution and emergence of novel flu viruses in the past decade.The following year (2017), 3 more viruses were added, and in june of 2018 the number jumped to 16 (see CDC Adds Two New Novel Viruses To Their IRAT List); 14 avian flu viruses, 1 Canine flu (H3N2) and 1 swine-variant flu virus (H3N2v).
The CDC uses two sets of criteria to evaluate novel viruses. One to estimate a virus's potential for sustained human-to-human transmission, and another to gauge it's potential for significant impact on public health.This past week, the CDC updated their IRAT list for the first time in nearly 2 years, adding 3 (2 swine-variant, 1 avian H9N2) new novel viruses. Ranked highest risk to low, they are:
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].
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].
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
The full list of the CDC's 19 novel flu viruses, ranked from most to least concern, follows:
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.
Sixteen of these 19 viruses have emerged over the past 9 years, and while not all of them are making headlines right now, they all exist in the wild and have shown some degree of pandemic potential.
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