#17,711
While avian flu activity has been somewhat subdued in the Northern Hemisphere over the summer, as we've increasingly seen over the past few years, it did not entirely go away.
This unusual persistence - combined with the expected return of migratory birds in the months ahead - suggests another busy fall and winter.
Which is one of the reasons why just over a week ago the EDCC announced plans for Targeted Surveillance to Identify Human Infections with Avian Influenza Virus during the Influenza Season 2023/24.
Admittedly, the number of human infections from clade 2.3.4.4b has been low compared to many previous years/clades (see WHO Chart below), but the unprecedented spillover into tens of thousands of mammals around the world (e.g. seals, sea lions, foxes, mink, pigs, etc.) has raised concerns.
Yesterday the U.S. CDC released an updated technical report (see previous March and May 2023 editions) on the avian H5N1 virus (see below), which attempts to consolidate what we know about this latest iteration (clade 2.3.4.4b) of this H5 virus.
This is a general reference document (with a lot of external links), which characterizes the current threat to the general public as `low', but warns that future viral evolution or reassortment events might might change that assessment.
Due to its length I've only posted some excerpts, so follow the link to read it in its entirety. I'll have a brief postscript after the break.
Technical Report: Highly Pathogenic Avian Influenza A(H5N1) Viruses
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Updated October 5, 2023
This report provides an update to the original report posted on March 17, 2023, to include additional sporadic human cases and activity in wild birds, poultry, and other animals. The overall risk to human health associated with the ongoing outbreaks of highly pathogenic avian influenza A(H5N1) viruses in wild birds and poultry has not changed and remains low at this time.
Executive summary
A small number of sporadic human cases of A(H5N1) have been identified since 2022, despite the panzootic of highly pathogenic avian influenza (HPAI) A(H5N1) viruses in wild birds and poultry. Nearly all reported human cases since 2022 were associated with poultry exposures, and no cases of mammal-to-human or human-to-human transmission of HPAI A(H5N1) virus have been identified. In a few cases, the source of exposure to HPAI A(H5N1) virus was unknown.To date, HPAI A(H5N1) viruses currently circulating in birds and poultry, with spillover to mammals, and those that have caused human infections do not have the ability to easily bind to receptors that predominate in the human upper respiratory tract. Therefore, the current risk to the public from HPAI A(H5N1) viruses remains low.However, because of the potential for influenza viruses to rapidly evolve and the wide global prevalence of HPAI A(H5N1) viruses in wild birds and poultry outbreaks, continued sporadic human infections are anticipated. Continued comprehensive surveillance of these viruses in wild birds, poultry, mammals, and people worldwide, and frequent reassessments are critical to determine the public health risk, along with ongoing preparedness efforts.
Key Points
- CDC is actively working on the domestic situation with clade 2.3.4.4b HPAI A(H5N1) viruses in wild birds and poultry outbreaks, including conducting surveillance among people with relevant exposures and preparing for the possibility that contemporary HPAI A(H5N1) viruses gain the ability for increased transmissibility to people.
- CDC, along with our state and local public health partners, continues to actively monitor people in the United States who have been exposed to infected birds and poultry for 10 days after exposure. To date, more than 6,500 people in 52 jurisdictions have been monitored since 2022, and only one human case has been identified.
- H5 candidate vaccine viruses (CVV) produced by CDC are expected to provide good protection against current clade 2.3.4.4b HPAI A(H5N1) viruses in birds and mammals. These H5 CVVs are available and have been shared with vaccine manufacturers.
- Because influenza viruses are constantly changing, CDC performs ongoing analyses of HPAI A(H5N1) viruses to identify changes that might allow for spread more easily to and between people, cause serious illness in people, reduce susceptibility to antivirals, affect the sensitivity of diagnostic assays, or reduce neutralization of the virus by vaccine induced antibodies. To date, few changes in HPAI A(H5N1) viruses of public health concern have been identified and such changes have differed between various HPAI A(H5N1) viruses circulating in wild birds and poultry worldwide or that have sporadically infected humans.
- Currently, HPAI A(H5N1) viruses circulating in birds are believed to pose a low risk to the general public in the United States; however, people who have job-related or recreational exposures to infected birds may be at higher risk of infection and should take appropriate precautions outlined in CDC guidance.
- Comprehensive surveillance and readiness efforts are ongoing, and CDC continually takes preparedness measures to be ready in case the risk to people from HPAI A(H5N1) or other novel influenza A viruses changes.
Table of Contents
Despite its recent geographic gains, and expanding host range, we've stood on the precipice before with H5N1, only to see the threat fizzle. Whether this clade has the `right stuff' to spark a pandemic remains unknown.
But H5N1 continues to evolve, and is fully capable of reassorting with a variety of avian, human, and swine influenza A viruses. A seasonal flu/avian flu hybrid might not prove as deadly, but it might spread a lot easier (see The `Other Mixing Vessel' For Pandemic Influenza).
Of course, there are a lot of plausible scenarios. And they aren't restricted to just H5 influenza viruses.
Since making predictions is a mugs game, I'll simply say there are an awful lot of moving viral parts out there - all on unpredictable, and largely unseen, evolutionary paths - and eventually one or more of them will coalesce into the next global public health threat.
The only thing we can really control is how prepared we'll be to deal with it when that happens.
