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Latest H7N9 epidemic biggest yet, new vaccines sought
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The latest H7N9 avian influenza epidemic to affect China is by far largest and most widespread, with 759 cases reported as of Aug. 7, according to researchers.
The epidemic included 281 deaths, and recent variations between viruses have prompted health care officials to develop several new vaccine candidates, researchers wrote in MMWR.
“These candidate vaccine viruses, as well as others being developed by other WHO collaborating centers for influenza, could be used for vaccine production, clinical trials, stockpiling and other pandemic preparedness purposes, based on ongoing public health risk assessment,” James C. Kile, DVM, from the CDC’s National Center for Immunization and Respiratory Diseases, and colleagues wrote.
This, the fifth H7N9 epidemic in China since March 2013, has brought the total number of cases to 1,557. Of those, at least 605 cases (39%) have resulted in death. The current epidemic has also reached “more provinces, regions and municipalities in China ... than during the first four epidemics combined,” the researchers said.
Recent mutations have yielded some high-pathogenic viruses, as well as some with reduced susceptibility to currently recommended antivirals.
The fifth epidemic has also revealed that the viruses have split into two lineages — the Pearl River Delta and Yangtze River Delta lineages. Viruses in the latter lineage have varied from those in earlier epidemics, the researchers said.
In an NIH trial, sera from patients who had received a vaccine produced with a 2013 virus had reduced antibody titers to high-pathogenic and Yangtze River Delta lineage viruses from the fifth epidemic.
In response to these revelations, in March, WHO recommended developing new candidate vaccine viruses (CVVs).
“The WHO Collaborating Center for the Surveillance, Epidemiology and Control of Influenza at CDC generated a new Asian H7N9 CVV derived from a Yangtze River Delta lineage low-pathogenic avian influenza virus,” Kile and colleagues wrote. “The WHO Collaborating Center for Reference and Research on Influenza in China developed a CVV from a high-pathogenic Asian H7N9 virus.”
They did not specify how close officials are to implementing those vaccines and several others in development.
Aside from vaccine development, officials are seeking to expand measures to prevent transmission of H7N9 viruses from birds to humans. The Chinese government is promoting large-scale farming, centralized slaughtering, and improvements in poultry product cold chain transportation and storage at markets, among other measures, the researchers said. They added that health care officials must continue to monitor virus developments.
“Although human infections with Asian H7N9 viruses from poultry are rare and no efficient or sustained human-to-human transmission has been detected, when human infections do occur, they are associated with severe illness and high mortality,” the researchers wrote. “Continued vigilance is important to identify changes in the virus that might have epidemiologic implications, such as increased transmission from poultry to humans or transmission between humans.” – by Joe Green
Disclosure: Kile reports no relevant financial disclosures. Please see the study for all authors’ relevant financial disclosures.
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