#15,946
For the second time in 2021 the CDC has added a new virus to their IRAT (Influenza Risk Assessment Tool) list, raising the number of zoonotic influenza viruses on their watchlist to a record high (n=21).
In February, the CDC added China's EA H1N1 `G4' swine virus, assigning it with the highest emergence score (n=7.5) to date.
- Potential Emergence Risk: The likelihood that a particular virus will become transmissible among humans
- Potential Impact Risk: And its impact (based on virulence, population immunity, etc.), should it become a pandemic strain
While IRAT can't predict which virus will become a pandemic strain (or when), it can help planners decide which viruses pose the greatest risks, so they can prioritize their efforts and investments.
Late this week, with little fanfare, the CDC updated their IRAT list, adding a 21st virus to the list - the avian H5N8 virus that made headlines last February following the announcement by Anna Popova, Chief State Sanitary Physician of the Russian Federation - of the first detection of human infection with this particular subtype (see Russian Media Reports 7 Human Infections With Avian H5N8).
Just twelve months ago, the CDC added three more viruses (2 swine-variant, 1 avian H9N2), bringing the total to 19. Over the past 6 years, the number of novel flu viruses on their list has nearly doubled.
While avian H5N8 has been sparking major epizootics since 2014, and there had been speculation that it might become zoonotic (see Virology: The Zoonotic Potential Of Multiple Subgroups of Clade 2.3.4.4. H5N8 Virus), until now we'd never seen confirmed human infections.
Since this announcement, we've see confirmation by the WHO and a risk assessment by the ECDC, both of which determined the risk of human infection to be low or very low. The CDC similarly ranks this virus as being moderate-to-low risk at this time.
Nevertheless, in early March the WHO prudently called for the development of a Candidate Vaccine Virus (CVV) against avian H5N8 (see WHO: Candidate Vaccine Viruses for Pandemic Preparedness - March 2021), just in case it becomes a more common zoonotic threat.
The IRAT masterlist, and details on the latest addition, follow.
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].
Those interested in how this virus was analyzed will want to follow the link to the full report.
While we are almost entirely focused on COVID-19 right now, it is worth noting that the CDC has added no fewer than 5 new flu viruses with zoonotic potential to their watchlist since the SARS-CoV-2 pandemic began.
Although we were blindsided by a coronavirus in late 2019, novel influenza continues to keep pandemic researchers up at night, as it has a long and storied history of successfully jumping species and sparking global epidemics.
Whether the next flu pandemic emerges from one of the viruses on the IRAT list - or comes (again) out of left field - we would do well to be far better prepared than we were going into COVID-19.