Saturday, July 01, 2023

CDC (Updated) Technical Report: Highly Pathogenic Avian Influenza A(H5N1) Viruses


 





#17,521

The CDC has released an updated technical report (see March edition) 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. 

Technical Report: Highly Pathogenic Avian Influenza A(H5N1) Viruses
 
Updated June 30, 2023

This report provides an update to the original report posted on March 17, 2023, to include information on 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 A(H5N1) viruses in wild birds and poultry has not changed and remains low at this time.


Executive summary

Despite the panzootic nature of highly pathogenic avian influenza (HPAI) A(H5N1) viruses in wild birds and poultry, only a small number of sporadic human cases of A(H5N1) have been identified since 2022. Nearly all reported human cases since 2022 were associated with recent 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 wide global prevalence of HPAI A(H5N1) viruses in wild birds and poultry outbreaks, continued sporadic human infections are anticipated. While U.S. flock outbreaks have declined substantially during spring and summer months, the ongoing global circulation of HPAI A(H5N1) viruses in wild birds, their ability to spread along migratory flyways and rapidly evolve warrants 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 current clade 2.3.4.4b HPAI A(H5N1) viruses associated with infections in wild birds and poultry outbreaks, including conducting surveillance among people with relevant exposures and preparing for the possibility that these HPAI A(H5N1) viruses gain the ability for increased transmissibility to people.
  • CDC, along with 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.
  • An H5 candidate vaccine virus (CVV) produced by CDC that is expected to provide good protection against current clade 2.3.4.4b HPAI A(H5N1) viruses in birds and mammals is available and has 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. No changes in current clade 2.3.4.4b HPAI A(H5N1) viruses in wild birds, poultry, mammals, or human cases have been identified that would suggest increased transmissibility to humans.
  • Currently, HPAI A(H5N1) viruses circulating in birds are believed to pose a low risk to the health of 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

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