H7N9 Virus

Influenza H7N9 – a summary of available information at 14 April 2013.

Prepared by Dr Alan Hampson 


There have now been 49 laboratory confirmed cases of influenza A(H7N9) virus in China, including 11 deaths, and the majority of cases are reported to be severe.  Some cases have a recorded symptom onset in late February and have been diagnosed retrospectively.  Further retrospective investigation of severe respiratory cases continues.  It is currently unclear whether there are a larger number of milder, as yet unidentified, cases.   Cases have occurred over a relatively wide area (see map) with a single case in Beijing but with a concentration in Shanghai.  No evidence has been found of person to person transmission but active contact tracing is being undertaken and the most recent case is husband to a woman who died of H7N9 on 3 April.

The Virus:

There have been human cases with H7 influenza in the past but bearing other neuraminidase types.  These have been mild respiratory infections often with conjunctivitis.  One death was recorded in The Netherlands in an apparently immunocompromised person.

H7 viruses exist as low pathogenic (LPAI) and highly pathogenic (HPAI) forms in poultry.  Previous human infections have usually involved HPAI viruses, the current virus is an LPAI strain.

Genetic analysis by Chinese scientists suggest that the virus is a genetic reassortant containing H7 and N9 genes derived from wild birds (possibly separately) and its remaining genes from an H9N2 influenza isolate also from a wild bird. Early reports indicate that the virus possesses some of the genetic characteristics that may favour adaptation to mammals. [http://www.nejm.org/doi/full/10.1056/NEJMoa1304459?query=OF#t=articleTop]

The virus is reported by the Chinese CDC to be sensitive to the neuraminidase inhibitors (Zanamivir and oseltamivir) and the Chinese have announced that they have licensed intravenous peramivir, a related antiviral, for use against it.

The Source:

To date the only notification (to the OIE) of a confirmed diagnosis was in a pigeon for sale as a food animal in a Shanghai market.  There are anecdotal reports of detection in ducks and chickens.  Poultry in a number of Shanghai markets have been slaughtered, and disposed of, and trading in live poultry halted.

The fact that the virus is LPAI and probably causing little or no disease in birds contributes to the difficulty of knowing how widespread it may be in poultry or other animals.  The distribution of cases may suggest that it is widespread.

Most of the cases/fatalities are middle-aged or elderly. A mild infection has been reported in the case of one child.  A number of the recorded cases have been in people with confirmed close contact with poultry or livestock (one a pork butcher).


A number of candidate H7 vaccine strains had been prepared previously as a part of the WHO pandemic preparedness program.  However, reports indicate that the current virus is sufficiently different to require a new vaccine strain.   Although they do not yet have a virus isolate CDC Atlanta and other groups are preparing candidate vaccine strains by synthesising antigens using genetic sequences posted on open databases by Chinese scientists.  They have estimated around a month will be required for the candidate vaccine strain to become available.

Risk analysis:

WHO have prepared a risk analysis and summary of known information – see: [http://www.who.int/influenza/human_animal_interface/influenza_h7n9/en/index.html

Australian perspective:

In the absence of human to human transmission there is little likelihood of an infected person arriving in Australia but travel history of acute respiratory illness in recently returned travellers is always important (note also the occurrence of novel coronavirus infections in people visiting the middle-east).

Chance of poultry/bird infections is essentially nil due to active quarantine and no evidence of migratory bird transmission of avian influenza from China to Australia.

H7N9: AusCMC Interview

Transcription of Australian Science Media Centre (AusSMC) interview with Dr Alan Hampson, Chair of the Australian Influenza Specialist Group.

4 April 2013

“At the moment it’s very hard to have any real idea of what is happening but the reports certainly are concerning. There is a virus out there, which like the H5N1 appears to be causing serious illness, how wide spread that illness is at this very early stage, we don’t know. We don’t know whether we’re seeing the tip of the iceberg or whether we’re actually seeing most of the cases as presenting as severe infection. If it’s the later then it’s a concern. The other thing is of course is there is no obvious source of the virus at the moment, undoubtedly it’s going to turn out to be domestic poultry, whether it’s chicken or ducks we don’t know. In the case of H5N1 in Thailand and Vietnam in 02/03 when people started to become ill, it was only after that that it was recognised that the virus was actually causing significant outbreaks in poultry. So maybe in the fullness of time it will be found this virus is also causing severe disease in poultry. If it isn’t and it is being transmitted amongst poultry without any obvious signs then that’s going to make it very difficult to get any idea of how you might control it, we have to wait and see and we have to wait to see if this is the tip of the iceberg in humans.”

About the particular H7N9 strain:

“The H7 virus has been known to cause mild infection in humans, been known to cause severe infections in poultry. But the particular neuraminidase type on this virus is different than we’ve seen reported. There have been 3 other neuraminidase types associated with the infections that have been in poultry and have transmitted to humans. So this H7N9, the N9 is the different aspect of this and whether that is contributing something to the virulence, we don’t know.”

Will this lead to a pandemic:

“No, we really hope not. If a virus starts to transmit amongst humans then there’s no telling how quickly it might travel and where it might travel too. We really don’t know, it’s very early days to know what we’re dealing with at this stage. Does it have pandemic potential, yes any influenza that jumps from an animal species to a human has pandemic potential. If it learns to spread in humans, if it actually acquires that ability, then it’s a high likelihood it will become pandemic. Can we do much about it? The world improved its pandemic responsiveness after the H1N1 outbreak but I think we have a long way to go in learning about this new strain.”


Page published: April 2013

Last updated:     April 2013