A novel strain of bird flu, H7N9 influenza A, has sickened 63 people and killed 13 in Shanghai and three surrounding provinces — Anhui, Zhejiang, and Jiangsu — health officials report, and scientists at the U.S. CDC are taking initial steps to prepare in the event of a pandemic.

“CDC takes routine preparedness actions whenever a new virus with pandemic potential is identified, including developing a candidate vaccine virus to make a vaccine if it were to be needed,” the agency said in a statement on it’s website.

Last Thursday, CDC officials and other U.S. scientists received their first specimens of H7N9 virus. Researchers are currently working to develop an antibody test, which would enable health care providers to tell if close contacts of known cases have been infected without getting seriously ill, as well as seed strains for a vaccine.

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So far, the majority of patients infected with H7N9 have reported contact with poultry, and here is no evidence of sustained ongoing human-to-human transmission necessary for a pandemic, according to WHO. But the virus’s rapid spread nearly 700 miles from the epidemic’s epicenter in Shanghai has some worried it may spread beyond China.

Based on previous experience with other avian influenza viruses, including H5N1, some limited human-to-human spread of this H7N9 virus would not be surprising, according to the CDC.

Although the virus has not yet demonstrated capability to easily and sustainably spread from person-to-person, “influenza viruses constantly change and it’s possible that this virus could gain that ability,” the agency warned.

Chinese authorities have begun testing domestic poultry and wild birds for H7N9. Thus far only 14 infected birds have been identified in five poultry markets located in the three affected provinces, a report published last week indicated. An additional two out of 10 ducks tested were also positive for H7N9, according to a separate report.

In the meantime, the CDC has issued guidance for how U.S. clinicians and public health departments should test for the virus, as well as interim guidance for case investigations and infection control procedures. At this time, no cases of human infection with H7N9 influenza A viruses have been detected in the United States. 

Concurrently, a profile of H7N9 is emerging. Yuelong Shu, PhD, of the Chinese CDC in Beijing, and colleagues published a report last week in New England Journal of Medicine outlining several characteristics of  H7N9 progression in three patients identified early in the outbreak.

All three patients had preexisting medical conditions: an 87-year-old man with chronic obstructive pulmonary disease and hypertension, a 27-year-old man with a history of hepatitis B virus infection and a 35-year-old woman with a history of hepatitis B virus infection, depression and obesity.

The course of illness was similar among all three patients, and consisted of rapidly progressing lower respiratory tract infections accompanied by fever, cough and dyspnea. The three patients ultimately died following the onset of acute respiratory distress syndrome and multi-organ failure, Shu and colleagues reported.

Other H7 influenza viruses identified in the past have generally caused mild disease in humans, whereas H7N9 appears to be causing mostly severe disease.

The researchers recommend treating patients with suspected or confirmed H7N9 infection with oseltamivir (Tamiflu) or zanamivir (Relenza), as testing shows the virus is susceptible to these drugs.

“The detection of human H7N9 virus infections is yet another reminder that we must continue to prepare for the next influenza pandemic,” Timothy M. Uyeki, MD, MPH, MPP, and Nancy J. Cox, PhD, of the U.S. CDC’s influenza division wrote in an accompanying NEJM editorial.

Because H7N9 influenza A infections have not occurred in humans before, it is expected that people of all ages might be susceptible worldwide, Uyeki and Cox warned.