Despite the rapid (and admittedly, concerning) spread and evolution of HPAI H7N9 in China over the past year, the virus's one saving grace is that it hasn't yet adapted well enough to human physiology to be able to transmit easily from human to human.
Whether that will ever happen is unknown, although a number of prominent researchers believe it could (see NPR: A Pessimistic Guan Yi On H7N9's Evolution).The CDC, via its IRAT (Influenza Risk Assessment Tool) Rankings, places two separate H7N9 strains at the very top of their list of novel viruses with pandemic potential, and the WHO continues to refine their Candidate Vaccines For Pandemic Preparedness.
In its present state, however, H7N9 remains only a local threat to public health in China. Today the ECDC released an updated Rapid Risk Assessment on the virus. The 15 page PDF file is chock full of data, graphs, charts and maps, so you'll want to download and read it in its entirety.
Below I've excerpted their main conclusions.
Conclusions and options for response
Since the notification of a novel reassortant influenza A(H7N9) virus on 31 March 2013, 1 548 laboratory-confirmed cases of human infection with avian influenza A(H7N9) virus have been reported. This is the fifth winter season in the northern hemisphere with human cases caused by A(H7N9) infections. During this wave, the number of human cases has been higher than in previous waves and accounts for 48% of the human cases reported so far.
The higher number of cases is most likely due to greater environmental contamination in live bird markets and increased circulation of the virus among poultry. In contrast to the situation observed during the summer months in previous years, A(H7N9) viruses are continuously circulating in the poultry population, with transmission to humans causing a substantial number of cases.
In February 2017, a new A(H7N9) virus with mutations in the haemagglutinin gene, indicating a change to high pathogenicity in poultry, was reported. This new variant virus has been detected in 25 of the 750 human cases in the current epidemic wave, but the cases were regionally restricted to three Provinces in China and did not show changes in severity. Highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI) A(H7N9) viruses co-circulate in the bird population.
Although the genetic changes in HPAI viruses may have implications in terms of pathogenicity, surveillance and control strategies for poultry, there is no evidence of increased transmissibility to humans or among humans to date. Data show that the newly emerged HPAI as well as some of the currently circulating LPAI viruses are genetically and antigenically distinct from current A(H7N9) candidate vaccine viruses. To address this, WHO has proposed new A(H7N9) candidate vaccine viruses.
Timely characterisation of A(H7N9) viruses and sharing of sequence information remains key for A(H7N9) vaccine virus development. HPAI A(H7N9) viruses from human cases have been found to have mutations associated with reduced susceptibility to neuraminidase inhibitors. Those mutations may have emerged during antiviral treatment. The proportion of viruses with reduced susceptibility to neuraminidase inhibitors has remained constant during the five recent epidemic waves.
The continued transmission of A(H7N9) to humans in China poses the risk that sporadic travel-related cases returning from China may be detected in Europe. The options for prevention and control of the infection outlined in the previous Rapid Risk Assessment remain valid:
- People travelling to China should avoid direct exposure to poultry and refrain from visiting live poultry markets or backyard farms.
- Travellers who have visited affected areas should be made aware that if they develop respiratory symptoms and fever upon their return, they should consult a physician and mention their recent travel history to enable early diagnosis and treatment.
In addition, travellers who have visited affected areas should avoid visiting farms after their return from affected areas in China for the entire duration of the 10-day incubation period (and during the symptomatic period in the event that they develop symptoms) in order to prevent a possible virus introduction to poultry in the EU. It cannot be excluded that humans infected with A(H7N9) return to the EU/EEA and introduce the virus. However, the risk of the disease spreading in Europe via humans is still considered low, as there is no evidence of sustained human-to-human transmission. EU/EEA Member States and the European Commission should consider relevant options – in terms of preparedness and communication – if sustained human-to-human transmission develops. Such options can include, but are not limited to the:
- development of plans for the identification, testing and follow-up of possible human cases
- continuation of influenza surveillance in poultry and wild birds for avian influenza viruses
- sensitisation of healthcare systems and confirmation of available surge capacity at healthcare facilities
- review of arrangements for delivery of relevant prevention and treatment measures.
Public health authorities need to maintain awareness of the virological and epidemiological features of the current A(H7N9) epidemic, including evidence from monitoring of transmission, severity, virus receptor binding and antiviral susceptibility properties.(Continue . . . . )
Of interest, the ECDC has created a list of `critical events' that, should one or more of them occur with H7N9 in China, they would likely have to re-evaluate their risk assessment.
Influenza A(H7N9) cases in humans and poultry continue to be reported. Case numbers are higher than during previous seasons, and the geographical spread has increased. ECDC decided to reassess the risk associated with this event and has established a list of critical events that would indicate a significant change in the epidemiology of the disease and trigger a reassessment of the situation:
• An increase in the size of human-to-human clusters beyond three cases
• An increase in the number and size of clusters related to nosocomial transmission in hospital settings
• An increase in the number of generations of human-to-human transmission beyond one
• An increase in the severity of reported cases, e.g. an increased case–fatality ratio
• Increase in the proportion of human cases infected with highly pathogenic A(H7N9) virus compared to low pathogenic virus
• A change in the epidemiology of A(H7N9) of infected human cases, e.g. different age groups
• The emergence of local transmission of A(H7N9) among poultry outside of China
• The emergence of locally infected human cases outside of China
• The detection of a human case in an EU/EEA healthcare facility
• Detection of A(H7N9) in wild birds
• Increasing, large and geographically widespread outbreaks or detections of highly pathogenic A(H7N9) virus in poultry
• Reassortment with other avian or seasonal viruses
• Molecular modification of viruses with markers for human adaptation
• Increase in antiviral resistance of viruses, also in humans without antiviral treatment.
ECDC actively monitors the situation, with a special focus on the occurrence of any of the above events.