A timely report in the MMWR today, particularly given the headlines in Hong Kong last night (see WHO warns of H7N9 pandemic), which provides a comparison of the most recent (4th) Epidemic wave of H7N9 to earlier waves.
While some changes in behavior have been detected, the virus has not demonstrated an ability to transmit efficiently from human-to-human.
The full MMWR review is quite detailed, and worthy of closer study, but a few highlights.
Assessing Change in Avian Influenza A(H7N9) Virus Infections During the Fourth Epidemic — China, September 2015–August 2016
Weekly / December 16, 2016 / 65(49);1390–1394
Nijuan Xiang, MD1*; Xiyan Li, MD2*; Ruiqi Ren, MD1*; Dayan Wang, PhD2; Suizan Zhou, MPH3; Carolyn M. Greene, MD3; Ying Song, MD3; Lei Zhou, MD1; Lei Yang, MD2; C. Todd Davis, PhD3; Ye Zhang, MD2; Yali Wang, MPH1; Jian Zhao, PhD1; Xiaodan Li, MD2; A. Danielle Iuliano, PhD3; Fiona Havers, MD3; Sonja J. Olsen, PhD3; Timothy M. Uyeki, MD3; Eduardo Azziz-Baumgartner, MD3; Susan Trock, DVM3; Bo Liu, MD1; Haitian Sui, MD1; Xu Huang1; Yanping Zhang, MD1; Daxin Ni, MD1; Zijian Feng, MD4; Yuelong Shu, PhD2; Qun Li, MD1
Since human infections with avian influenza A(H7N9) virus were first reported by the Chinese Center for Disease Control and Prevention (China CDC) in March 2013 (1), mainland China has experienced four influenza A(H7N9) virus epidemics.
Prior investigations demonstrated that age and sex distribution, clinical features, and exposure history of A(H7N9) virus human infections reported during the first three epidemics were similar (2). In this report, epidemiology and virology data from the most recent, fourth epidemic (September 2015–August 2016) were compared with those from the three earlier epidemics.
Whereas age and sex distribution and exposure history in the fourth epidemic were similar to those in the first three epidemics, the fourth epidemic demonstrated a greater proportion of infected persons living in rural areas, a continued spread of the virus to new areas, and a longer epidemic period.
The genetic markers of mammalian adaptation and antiviral resistance remained similar across each epidemic, and viruses from the fourth epidemic remained antigenically well matched to current candidate vaccine viruses.
Although there is no evidence of increased human-to-human transmissibility of A(H7N9) viruses, the continued geographic spread, identification of novel reassortant viruses, and pandemic potential of the virus underscore the importance of rigorous A(H7N9) virus surveillance and continued risk assessment in China and neighboring countries.
From the Discussion:
There is no evidence of increased transmissibility of A(H7N9) virus from poultry or environmental exposures to humans in China or sustained human-to-human transmission; however, using the Influenza Risk Assessment Tool (10), CDC found that A(H7N9) virus has the highest potential pandemic risk of any novel influenza A viruses that have been assessed.
The recent geographic spread, the identification of divergent virus lineages, and the pandemic potential of the virus underscore the importance of effective A(H7N9) virus surveillance and continued risk assessment among humans and poultry in China and neighboring countries.