Reports on China’s recent response to the outbreak of novel influenza have reflected broad international satisfaction. While we share this satisfaction, we are nonetheless concerned that the international public health community overestimates China’s ability to effectively contain and control a future returning, or newly occurring influenza outbreak.
The influenza virus – a leading cause of infectious disease in animals and humans – is a cause of ongoing apprehension among national and international public health officials because of its propensity for mutation. While the structure of the virus changes modestly on a continuous basis, on rare occasions major mutations in key genes lead to a virus with either a new host range or a heightened propensity to cause serious (and perhaps life-threatening) complications such as pneumonia or multiple organ system failure. Both have occurred with the arrival in China of a novel influenza virus called H7N9. (“H” and “N” refer to the molecules on the surface of virus particles that determine its ability to infect the cells of potential hosts, and the numerals designate the specific structure of those molecules. The combination of a particular H and N is called an influenza “subtype”). This still-evolving story is a mixture of some public health successes but also many unanswered question.
Novel H7N9 virus was first identified sometime in late March of this year after three individuals died from severe respiratory disease: two in Shanghai and one in Anhui province. Scientists at China’s National Influenza Center isolated a virus from samples taken from these patients that tested as an influenza virus of unknown subtype. Genetic sequencing revealed a virus comprising the genetic material of at least three influenza viruses that previously only infected birds, and had never infected humans. The new virus was immediately reported to the World Health Organization. The apparent direct transmission of this virus from a bird host (probably a chicken) along with the high mortality rate immediately raised the possibility of a new pandemic virus, should it become capable of human-to-human transmission.
The response of the Chinese Centers for Disease Control was swift: Tens of thousands of poultry in thousands of farms were tested for the virus, along with pigs (this species is often susceptible to new influenza viruses) and poultry workers. Live bird markets in major cities were shut down, and an extensive symptom survey of contacts of known influenza victims and many hundreds of poultry workers in the eastern Chinese provinces along with blood testing was completed in fewer than four weeks. All individuals with severe respiratory illness were admitted to large medical centers and received up-to-date treatment. Chinese (and other) virologists began work to develop an H7N9-specific vaccine. China also invited international public health experts into the country and quickly shared available information on the virus with the international community.
As of July 2013, 132 known human cases had been identified with 43 deaths, resulting in an overall mortality of about 33%. No clear human-to-human transmission has yet occurred. The outbreak among humans may have reached its nadir, with only one case reported in May and one case in mid-July. It is to this outcome that the international community points when praising China for its pandemic response.
However, this is unlikely to be our last encounter with H7N9. It is almost certain that new cases will appear later in the year as temperatures fall. (The virus is fragile, and when deposited on surfaces, its infectiousness is limited by high temperatures).