On April 1, 2013, the World Health Organization (WHO) reported three human infections with avian influenza A (H7N9) viruses in China. This is the first time avian influenza A (H7N9) viruses have been detected in humans. Each of the three confirmed cases had severe respiratory illness; two of them died. According to WHO, no human-to-human transmission has been identified at this time, and the cases do not have a known epidemiological link to one another.
An investigation by Chinese health authorities is ongoing to determine the source of infection and detect any additional cases. The sequences of these viruses are posted and publicly available in GISAIDExternal Web Site Icon.
CDC is following this situation closely and coordinating with domestic and international partners in a number of areas, including gathering more information to make a knowledgeable public health risk assessment and developing a candidate vaccine virus. CDC also is reviewing posted genetic sequencing of the new H7N9 viruses and assessing possible implications in terms of the viruses’ transmissibility and severity and whether existing influenza diagnostic tests need to be enhanced or new ones developed. All of these actions are routine preparedness measures taken whenever a new novel influenza virus is detected in humans.
This is an evolving situation and there is still much to learn. It is too soon to speculate regarding the significance of these cases/viruses, however, CDC will provide updated information as it becomes available.