#17,355
Over the past several months we've see a flurry of technical documents on HPAI H5N1 clade 2.3.4.4b come out of the WHO, ECDC, UKHSA, and the CDC, including:
Canada: Updated Public Health Guidance On Avian H5N1 For Healthcare Professionals
WHO Update & Risk Assessment On Human H5N1 Infection - Ecuador
WHO Rapid Risk Assessment on A(H5N1) clade 2.3.4.4b viruses (Includes 2 Severe/Fatal Human Infections)
UK HSA Technical Briefing: Risk Assessment On HPAI H5N1 & Human Infection
ECDC Guidance For Testing & Identification Of Zoonotic Influenza Infections In Humans In The EU/EAA
With every passing week new information on outbreaks in poultry, spillovers into mammals, and sporadic human infections emerges, necessitating frequent updates.
Today the CDC has published their latest technical report on H5N1 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 March 17, 2023
Executive summary
Since 2022, despite the wide geographic spread of highly pathogenic avian influenza (HPAI) A(H5N1) viruses in wild birds and to poultry worldwide, with sporadic spillover to mammals, only a small number of sporadic human cases of A(H5N1) have been identified. All reported human cases since 2022 were associated with recent poultry exposures, and no cases of human-to-human transmission have been identified. 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 6,300 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 is nearly identical or, in many samples, identical to the hemagglutinin (HA) protein of recently detected clade 2.3.4.4b HPAI A(H5N1) viruses in birds and mammals (including the recent outbreak in farmed mink in Spain) and could be used to produce a vaccine for people, if needed, and would provide good protection against the clade 2.3.4.4b HPAI A(H5N1) viruses circulating in birds. This H5 CVV is available and has been shared with vaccine manufacturers.viral evolution or reassortment events which might change the current risk assessment.
- Because influenza viruses are constantly changing, CDC performs ongoing analyses of A(H5N1) viruses to identify genetic 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, no such concerning changes have been identified in HPAI A(H5N1) viruses circulating in wild birds and poultry worldwide or that have sporadically infected humans.
- Currently, HPAI A(H5N1) viruses 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.
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Limitations of the Report
This report is subject to the following limitations. First, the number of human infections with currently circulating clade 2.3.4.4b HPAI A(H5N1) viruses is small. Conclusions regarding virus characterization analyses, transmissibility from animals to people, transmissibility among people, and clinical spectrum of illness in people should be interpreted in light of this small number. Second, detailed exposure information was not available for all persons actively monitored for illness after exposure to HPAI A(H5N1) virus-infected birds and poultry in the United States. Thus, we were not able to assess the impact of exposure variables such as duration of exposure, nature of exposure (e.g., direct vs. indirect contact), and use of personal protective equipment on infection risk.
Conclusions
- To date, CDC analyses of clade 2.3.4.4b HPAI A(H5N1) viruses detected in wild birds, poultry, and sporadically in mammals since late 2021 indicate that these viruses all have a high degree of genetic identity with each other and no significant mammalian adaptive substitutions, insertions or deletions have been identified, particularly in the HA gene, which is important for zoonotic and subsequent human-to-human transmission.
- Considering the high prevalence of HPAI A(H5N1) viruses detected in wild birds, and poultry worldwide, spill over into mammals (particularly carnivores that may feed on infected avian species), additional sporadic zoonotic infections among people with exposures to sick or dead poultry or wild birds are anticipated.
- HA clade 2.3.4.4b A(H5N1) viruses currently circulating in wild birds and poultry worldwide lack the ability to preferentially bind to the types of sialic acid receptors that are predominant in the upper respiratory tract of humans and therefore do not currently have the ability to easily infect or transmit among people.
- Despite extensive worldwide spread of influenza A(H5N1) viruses in wild birds and poultry in recent years, only a small number of sporadic human infections with 2.3.4.4b or clade 2.3.2.1c H5N1 viruses have been reported since 2022; all cases had recent exposure to poultry and no cases of human-to-human influenza A(H5N1) virus transmission were identified.
While CDC’s assessment is that the overall threat of HA clade 2.3.4.4b A(H5N1) viruses to public health is currently low, the widespread geographic prevalence of infected birds and poultry raises the potential for exposures of humans and other mammals that could result in viral evolution or reassortment events which might change the current risk assessment. Vigilance and ongoing surveillance of HPAI A(H5N1) viruses circulating in wild birds, poultry, and in sporadic infections of mammals and people worldwide is critical to monitor the public health risk and to detect genetic changes (particularly in the HA gene) that would change CDC’s risk assessment.
