WHO Novel Flu Summary & Risk Assessment - July 23rd to Aug 8th

WHO IHR Infographic  

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Since my update on India's confirmed H5N1 human infection a few hours ago, the World Health Organization has published their latest Influenza at the human-animal interface summary covering the time period from June 23rd to August 8th. 

While COVID-19 remains our primary focus right now, there are literally dozens of novel flu subtypes/clades in circulation around the world that have zoonotic potential. Surveillance and reporting on these viruses is limited even during the best of times, but is probably even more compromised during this pandemic.

All of these viruses, whether they are on our radar or not, continue to evolve with many of them showing evidence of increased adaptation to mammals. Last May, the CDC Added Zoonotic Avian A/H5N8 To Their IRAT List, and over the winter we saw the biggest HPAI H5 epizootic in Europe since their historic outbreak of 2016-17. 

Also in May, in Science: Emerging H5N8 Avian Influenza Viruses, we looked at a review by two well-respected Chinese scientists (Weifeng Shi and George F. Gao)  on the evolution, and growing zoonotic threat, of avian H5N8, stating:

•  the  ". . . global spread of AIVs, particularly the H5N8 subtype, has become a major concern to poultry farming and wildlife security but, critically, also to global public health."
• And due to the ". . . long-distance migration of wild birds, the innate capacity for reassortment of AIVs, the increased human-type receptor binding capability, and the constant antigenic variation of HPAIVs  the authors warned that it was imperative that " . . . the global spread and potential risk of H5N8 AIVs to poultry farming, avian wildlife, and global public health are not ignored."

In June, in V. Evolution: Genomic Evolution, Transmission Dynamics, and Pathogenicity of Avian H5N8 Viruses Emerging in China, 2020, we saw Chinese researchers describe the rapid rise in 2020 of an antigenically distinct H5N8 virus that is lethal to chickens and mice, that is similar to the Russian Zoonotic strain, and has shown signs of mammalian adaptation.

It is against this backdrop that we are seeing an uptick in human avian H5 infections, with the WHO confirming 6 H5N6 cases (see blogs here, here, and here) and 1 H5N1 case in the latest reporting period. 

Influenza at the human-animal interface Summary and assessment, from 23 June to 8 August 20211 

• New infections2 : Since the previous update on 22 June 2021, one human case of infection with an avian influenza A(H5N1) virus and six human cases of infection with avian influenza A(H5N6) viruses were reported officially. 3

 • Risk assessment: The overall public health risk from currently known influenza viruses at the human-animal interface has not changed, and the likelihood of sustained human-to-human transmission of these viruses remains low. Human infections with viruses of animal origin are expectedat the human-animal interface wherever these viruses circulate in animals. 

• IHR compliance: All human infections caused by a new influenza subtype are required to be reported under the International Health Regulations (IHR, 2005). 4 This includes any influenza A virus that has demonstrated the capacity to infect a human and its haemagglutinin gene (or protein) is not a mutated form of those, i.e. A(H1) or A(H3), circulating widely in the human population. Information from these notifications is critical to inform risk assessments for influenza at the human-animal interface. 

Avian Influenza Viruses Current situation: Avian influenza A(H5) viruses 

Since the last risk assessment on 22 June 2021, one new laboratory-confirmed human case of influenza A(H5N1) was reported from India to WHO. In July 2021, an 11-year-old boy from Haryana State had onset of respiratory symptoms and was admitted to hospital. He had been recently diagnosed with an underlying immunodeficiency and rapidly deteriorated and passed away on 12 July 2021. A sample collected during his hospitalization tested positive for influenza A(H5N1) and influenza B/Victoria lineage viruses. The source of his exposure to the influenza A(H5N1) virus is unknown at this time. No further cases are suspected among his close contacts. This is the first human case of infection with an avian influenza A(H5N1) virus reported from India. 

Figure 1: Epidemiological curve of avian influenza A(H5N1) cases in humans by month of onset, 2003-2020

Since the last risk assessment on 22 June 2021, six cases of influenza A(H5N6) virus infection were reported from China to WHO.

All cases were sporadic infections due to exposure to live poultry or live poultry markets. No suspected cases were detected among close contacts of these cases at the time of reporting. The 61- year-old woman who had mild illness was detected through influenza-like illness (ILI) surveillance.

 According to reports received by the World Organisation for Animal Health (OIE), various influenza A(H5) subtypes continue to be detected in birds in Africa, Europe and Asia. 

Risk Assessment: 

1. What is the likelihood that additional human cases of infection with avian influenza A(H5) viruses will occur? 

The overall risk assessment is unchanged. Most human cases were sporadic infections exposed to A(H5) viruses through contact with infected poultry or contaminated environments, including live poultry markets. Since the viruses continue to be detected in animals and related environments, 3 further human cases can be expected. The detection of influenza A(H5) virus in nasopharyngeal/oropharyngeal samples collected from individuals in close contact with infected poultry or other birds, whether the individuals are symptomatic or not, is not unexpected. Good quality serological investigations may be useful in differentiating infection from localized contamination (not true infection) in these cases and allow for better assessment ofthe risk of human infection. 

2. What is the likelihood of human-to-human transmission of avian influenza A(H5) viruses? 

Even though small clusters of A(H5) virus infections have been reported previously including those involving health care workers, current epidemiological and virological evidence suggests that influenza A(H5) viruses have not acquired the ability of sustained transmission among humans, thus the likelihood is low. 

3. What is the risk of international spread of avian influenza A(H5) viruses by travellers? 

Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as evidence suggests these viruses have not acquired the ability to transmit easily among humans.

(Continue . . . )

H5N1 outbreaks, and human infections, are nowhere near their peak of 2014-2015, and while H5N6 cases are increasing, we've yet to see any evidence of human-to-human transmission.  For now, these zoonotic avian viruses remain a limited, localized threat - primarily in Asia - to those who have close contact with poultry. 

But H5 avian influenza viruses have a long track record of producing serious - often fatal - infections in humans, and they continue to evolve.  Each human infection is another opportunity for the virus to better adapt to human physiology, and perhaps even a reassortment opportunity, if the host is co-infected with seasonal influenza A. 

Given the limits of surveillance, testing, and reporting it is unlikely that we are hearing about all of the avian flu outbreaks, and human infections, that occur around the globe (see Flying Blind In the Age Of Pandemics & Emerging Infectious Diseases).

Hence the following advice from the WHO. 

Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virologic, epidemiologic and clinical changes associated with circulating influenza viruses that may affect human (or animal) health. 

Continued vigilance is needed within affected and neighbouring areas to detect infections in animals and humans. Collaboration between the animal and human health sectors is essential. As the extent of virus circulation in animals is not clear, epidemiological and virological surveillance and the follow-up of suspected human cases should remain high.

Guidance on investigation of non-seasonal influenza and other emerging acute respiratory diseases has been published on the WHO website here: https://www.who.int/publications/i/item/WHO-WHE-IHMGIP-2018.2. 

• In the current COVID-19 pandemic, vigilance for the emergence of novel influenza viruses of pandemic potential should be maintained. WHO is developing practical guidance to prepare for the upcoming influenza season and influenza emergencies in the context of the cocirculation of SARS-CoV-2 and influenza viruses.