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WHO H7N9 H5N8 Presser March 1


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WHO Media Advisory
28 February 2017
 
 
INVITATION TO A VIRTUAL PRESS CONFERENCE
 
 
WHO expert briefing on the current waves of Avian Influenza outbreaks 
 
 
WHAT: The current 5th wave of the avian influenza H7N9 outbreak in China as well reoccurring outbreaks of avian influenza H5N8 in Europe have raised the level of concern.
 
A panel of experts will be discuss the recent development and provide a risk assessment for the different outbreaks.
 
WHEN: Wednesday 1 March 2017 at 07:30 EST (New York time) / 12:30 GMT (London time) / 13:30 CET (Geneva time)
 
SPEAKERS:
Chair: 
  • Dr Wenqing ZHANG; Head, Global Influenza Programme, WHO HQ
Experts: 
  • Dr Jackie KATZ; Director, WHO CC, CDC Atlanta, USA
  • Dr Yuelong SHU; Director, WHO CC, China CDC, Beijing, China
 
Journalists are invited to dial in to the briefing (phone-in details below).
 
==================================================================================
 
How to access the virtual press conference:
 
Please try to call in at least 10 minutes before the conference begins in order to be registered correctly. From the list below, please use the number closest to you. If you have problems with a number, try the toll number from a neighbouring country or call Switzerland: +41 22 580 59 70, or France +33 1 70 75 07 05, or the United States +1 855 402 77 66. You can also use a VoIP programme such as Skype to call the US toll-free: +1 855 402 77 66
 
On connecting, type PIN code: 16204291# on your telephone keypad, then record your name and media outlet and then press the # keyagain.
 
To ask a question during the question and answer session, registered participants should type 01 on their telephone keypad. This will place you in the queue to ask questions.

 

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How to access the virtual press conference:
 
Please try to call in at least 10 minutes before the conference begins in order to be registered correctly. From the list below, please use the number closest to you. If you have problems with a number, try the toll number from a neighbouring country or call Switzerland: +41 22 580 59 70, or France +33 1 70 75 07 05, or the United States +1 855 402 77 66. You can also use a VoIP programme such as Skype to call the US toll-free: +1 855 402 77 66
 
On connecting, type PIN code: 16204291# on your telephone keypad, then record your name and media outlet and then press the # keyagain.
 
To ask a question during the question and answer session, registered participants should type 01 on their telephone keypad. This will place you in the queue to ask questions.
 
International access numbers
 
COUNTRY TOLL-FREE TOLL
Argentina   +541152526531
Australia   +61291011917
Austria   +4319280492
Belgium   +3211500307
Brazil   +551138788007
Canada   +14162164186
China   4006815483
Czech Rep   +420225439711
Denmark   +4535445572
Finland   +358981710496
Estonia 8000111813  
France 0805110449 +33170750705
Germany 08006270715 +4969222229043
Hong Kong   +85230773565
Hungary   +3612354718
India   +912261875155
Ireland   +35314475417
Israel   +97237207689
Italy   +390236013806
Japan   +81344556490
Luxembourg   +35227300157
Malaysia   +60320531818
Mexico 018002822715  
Netherlands   +31107137273
Norway   +4723500249
Poland   +48225839013
Russia   +74956469303
Saudi Arabia 8008143582  
Singapore   +6564298337
South Africa   +27216724108
Republic of Korea 00308123559  
Spain   +34911140084
Sweden   +46850556469
Switzerland 0800005200 +41225805970
Turkey   +902123755118
UAE 800035704060  
United Kingdom   +442030092452
USA 18554027766  
 
==================================================================================
 
Media contacts:
   
Shortly after the Virtual Press Briefing, an audio file will be sent to the media distribution list.
 
All WHO information can be found at: www.who.int
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Dear journalists,


Please find below the introduction remarks by Dr  Wenqing ZHANG; Head, Global Influenza Programme, WHO HQ.

Statement at virtual press conference on H7N9 and other avian influenzas

1 March 2017



Thank you Christian and thanks to the journalists for joining us on the line. 

Today, we would like to provide an update on influenza H7N9 and other avian influenzas, giving you the current situation: what is different from previous years, what the associated risk is, and what WHO’s recommendations and actions are. We are taking the opportunity of doing this because of the presence in Geneva this week of directors of two WHO Collaborating Centres on Influenza. They will speak with you as well.

Risk assessment
Before we get into the details, our core message is that the risk of sustained human-to-human transmission of H7N9 remains low, as it does for other subtypes of avian influenzas. However, constant change is the nature of all influenza viruses, and that is why we follow the developments so closely.
 
H7N9 in humans this year
WHO constantly monitors zoonotic infections, meaning infections in animals that can naturally transmitted to humans. This year, we have closely followed the fifth wave—which is the current wave—of H7N9 in humans. H7N9 is an avian influenza that was first reported in 2013. From October 2016 to today, there have been a total of 460 laboratory-confirmed human infections with A(H7N9), reported to us from China. The number exceeds previous seasons and accounts for more than 1/3 of total cases since 2013. However, the epidemiological characteristics of human infections, such as the sex ratio, exposure history, case fatality rate, the median age of human cases … remain similar to previous waves.
 
What is new 1?
In this 5th wave, viruses from about 7% of human cases have had genetic markers associated with resistance to neuraminidase inhibitors. Neuraminidase inhibitors are a category of antivirals, including Oseltamivir, for case management (or treatment) of influenza infection.  This rate is similar to previous waves. Although a slight increase was observed, it is still lower than that of 1st wave according to data from WHO Collaborating Centre in China CDC Beijing. Notably, since 2013, except for one environmental virus, all antiviral resistant viruses were from human cases. From information available, most cases were sampled after treatment with antivirals. This means that most of the resistant viruses were developed after the use of antivirals in patients, and not before.  WHO is closely monitoring these developments. So far there is no evidence to recommend changes in clinical management of the infection.
 
What is new 2 ?
Based on genetic information available in the GISAID EpiFlu database, which is a publically accessible database that gathers information of influenza viruses from around the world, viruses from 3 recent human cases and 1 environmental specimen have changes. These changes make the virus highly pathogenic in birds, meaning that it can cause some severe disease in birds. Previously, H7N9 had only been observed to be “low pathogenic” in birds, meaning the virus did not cause visible outbreaks of disease in birds.
 
Again, classification of pathogenicity here refers to birds, not to humans. At this time, there is no evidence that these changes in the virus affect its pathogenicity or transmissibility in humans.
 
Other avian influenza viruses
A quick note on other avian influenza viruses: aside from H7N9, H5 viruses in the format of H5+N1, 2, 3, 5, 6, 8 and 9 continue spreading in avian population, though so far only H5N1 and H5N6 cause human infections. The assessment of the risk of sustained human to human transmission of the H5 viruses remains low.

WHO response
Since 2003 with the emergence of the highly pathogenic avian influenza H5N1, WHO has been providing updates of the situation, the risk assessment and risk management recommendations to Member States on avian influenza.
 
WHO, working through the Global Influenza Surveillance and Response System (GISRS), in collaboration with the agricultural and animal health sectors and organizations such as FAO, OIE, as well as other institutions, has been closely monitoring the virus evolution, conducting risk assessment, updating laboratory diagnostics, strengthening surveillance globally and adjusting control measures, such as selecting and developing new candidate vaccine . WHO is also strengthening capacity in countries, and negotiating access to pandemic vaccines and stockpile of antivirals.  And we will continue this work.
 
Prevention
WHO’s prevention advice remains the same: avoid, if possible, poultry farms, contact with animals in live bird markets, entering areas where poultry may be slaughtered, or contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Follow good hand hygiene and food safety practices: wash your hands often with soap and water, cover your mouth and nose when coughing or sneezing, cook food thoroughly.

Conclusion
The risk of sustained human to human transmission of H7N9 and H5 avian influenzas remains low. It is highly likely that further sporadic cases will continue to be reported, as long as the viruses continue circulating in poultry. WHO, through its Global Influenza Surveillance and Response System (GISRS) and working with other partners, is monitoring the situation very closely. Constant change is the nature of all influenza viruses – this makes influenza a persistent and significant threat to public health.

Best regards,
WHO Media Team

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WHO says bird flu outbreaks raise alarm, but human risks still low

 
 
 
  •  
  •  
  •  
  •  
By Kate Kelland | NDON,

- LOThe risk of sustained human-to-human transmission of H7N9 bird flu in China is low, the World Health Organization said on Wednesday, but a surge in human cases there is worrying and requires constant monitoring.

Outbreaks of H5 bird flu strains in poultry and wild birds across Europe, Africa and Asia are also raising concern, the WHO said, and while the human risk of these outbreaks is also low for now, vigilance is vital.

"Constant change is the nature of all influenza viruses – this makes influenza a persistent and significant threat to public health," Wenqing Zhang, head of the WHO's global influenza program, told reporters on a telephone briefing.

China is currently seeing a fifth wave of H7N9 bird flu in humans - a virus that was first detected in people in 2013.

Since October 2016, a total of 460 laboratory-confirmed human H7N9 infections have been reported in China, a figure that exceeds previous seasons and accounts for more than a third of total cases since 2013. So far, H7N9 has killed around a third of people it has been known to infect.

While this surge is concerning, the WHO said, there is still no evidence that the epidemiological characteristics of human infections - such as the age and gender of those infected, their exposure history and the case fatality rate - are changing.

Zhang noted, however, that around 7 percent of the human cases of H7N9 this year are showing resistance to anti-viral drugs known as neuraminidase inhibitors. These medicines, including Roche's well-known drug Tamiflu, or oseltamivir, are recommended as flu treatments.

The WHO said it was watching these developments, but said there was no reason to recommend changes in how patients are treated for now.

With H5 bird flu strains, multiple outbreaks have been reported in poultry farms and wild flocks across Europe, Africa and Asia in the past three months. The WHO said more than 1,000 outbreaks had been reported to the United Nations Organization for Animal Health (OIE) in Paris.

Most involve strains that are low risk for humans, but virologists and public health specialists are worried that the sheer number of different types and their presence in so many parts of the world at the same time, increases the risk of viruses mixing and mutating, and possibly jumping to people.

The WHO noted that "so far, only H5N1 and H5N6 cause human infections", but said it was working with the OIE to monitor the viruses' evolution.

 

(Reporting by Kate Kelland; Editing by Robin Pomeroy and Richard Lough)

http://www.reuters.com/article/us-birdflu-who-idUSKBN1684GZ

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Mar 1, 11:04 AM EST
 

UN SEES BIRD FLU CHANGES BUT CALLS RISK OF PEOPLE SPREAD LOW


AP Photo
AP Photo/Kin Cheung
 
 
 
 
A

LONDON (AP) -- The World Health Organization says it has noticed changes in the bird flu virus now spreading in China, but says the risk of the disease spreading easily between people remains low.

The genetic mutations have been seen from birds and infected people, but because flu viruses change constantly, experts aren't exactly sure how significant the differences may be.

The H7N9 strain of bird flu showed up in China in 2013 and has mainly sickened people in close touch with chickens or other infected people.

In a press briefing Wednesday, the U.N. health agency said in about 7 percent of recent cases, scientists have identified genetic changes suggesting the viruses are resistant to Tamiflu, the recommended treatment for the illness. The drug is being stockpiled worldwide in case there is a flu pandemic, possibly triggered by a mutated bird flu virus.

Wenqing Zhang, head of WHO's flu department, said the rate is similar to what has been picked up in previous years.

"Constant change is the nature of all influenza viruses," she said.

Zhang said the mutations in the H7N9 virus have made it more deadly to birds, but she said it's unclear what that might mean for humans.

"The question is, does this change in the virus' lethality make it any more lethal for humans? The jury is still out on that," said Wendy Barclay, a professor at Imperial College London.

Although bird flu cases in China have surged this year - and spilled over to Hong Kong and Taiwan - Barclay said there was no suggestion the virus is spreading more easily, particularly among people.

Since October, 460 people in China have been infected, WHO said. That's more than one-third of the 1,250 infections reported since 2013.

Some scientists worry that China isn't sharing enough information. Earlier this year, the country suddenly announced about 100 cases, a lag that could compromise efforts to track any changes in the virus' spread.

"We always need more and better information faster," said Michael Osterholm of the University of Minnesota, adding that the continuing bird flu worries underline the world's vulnerability to the next flu pandemic.

http://hosted.ap.org/dynamic/stories/E/EU_MED_BIRD_FLU?SITE=AP&SECTION=HOME&TEMPLATE=DEFAULT

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WHO sees bird flu changes, calls risk of spread in people low

Mutations in the H7N9 bird flu virus have made it more deadly to birds

The Associated Press Posted: Mar 01, 2017 8:53 AM ET Last Updated: Mar 01, 2017 9:00 AM ET

H7N9 is an avian influenza that was first reported in 2013.

H7N9 is an avian influenza that was first reported in 2013. (Associated Press)

The World Health Organization says it has noticed mutations in the bird flu virus that is now spreading in China, but says the risk of the disease spreading easily between people still remains low.

In a press briefing Wednesday, the U.N. health agency said in about 7 per cent of the people infected with the H7N9 strain of bird flu, scientists have identified genetic changes suggesting the viruses are resistant to Tamiflu, the recommended treatment for the disease.

 Wenqing Zhang, head of WHO's flu department, said the rate is similar to what has been picked up in previous years.
 
"Constant change is the nature of all influenza viruses," she said. Zhang said that the resistant viruses were detected in people who had already been treated with Tamiflu, allaying fears that the virus might be spontaneously acquiring resistance in the wild. 
 
Zhang said mutations in the H7N9 virus have also made it more deadly to birds, but he says it's unclear what that might mean for humans. 
 
Other experts said that the increased danger of H7N9 to birds would at least make the disease easier to spot in poultry, allowing officials to react quicker.
 
 "The question is, does this change in the virus' lethality make it any more lethal for humans? The jury is still out on that," said Wendy Barclay, chair of influenza at Imperial College London. 
 
Although bird flu cases have surged this year, Barclay said there was no suggestion the virus is adapting more easily to human transmission. "Based on the genetic sequences of the viruses, there are no changes to suggest this is about to explode into a pandemic," Barclay said. 
 
Some scientists have raised concerns about whether China is sharing enough information; earlier this year, the country suddenly announced about 100 cases, a lag that could compromise efforts to track any changes in the virus' spread.
 
"We always need more and better information faster," said Michael Osterholm of the University of Minnesota, adding that the continuing bird flu worries underline the world's vulnerability to the next flu pandemic. 
 
"We are not in any better position to respond than we were during the (2009) swine flu pandemic," he said.

http://www.cbc.ca/news/health/bird-flu-1.4004338

 

 

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H7N9 Flu Outbreak Largest Yet

But risk of sustained transmission among people remains low: WHO

  • by 
    North American Correspondent, MedPage Today
 

The current wave of H7N9 avian flu in China is the largest yet and accounts for more than a third of the human cases recorded since the strain was identified in 2013, according to an official of the World Health Organization.

But most other characteristics of the current outbreak, now standing at 460 cases, are similar to earlier waves, including the median age of patients, their history of exposure to poultry, and the risk of dying from the disease, said Wenqing Zhang, MD, head of the agency's global influenza program.

Risk of sustained transmission between people remains low, she told reporters in a telephone briefing, but "constant change is the nature of all influenza viruses (making) influenza a persistent and significant threat to public health."

Avian H7N9 influenza was identified in humans in 2013 and experts were concerned at the time that it had two of the three characteristics that could lead to a pandemic -- it was able to infect people and because it was new few people had any immunity to it.

The missing link was the ability to spread efficiently among people and so far, Zhang said, the virus hasn't acquired that capacity.

The current outbreak in China appears to have peaked, commented Yuelong Shu, PhD, director of the WHO Collaborating Center on influenza at the China Center for Disease Control in Beijing.

But Zhang said it's "highly likely" that more sporadic cases will be reported, because the virus is still circulating in poultry in China and people shopping in live poultry markets are likely to be exposed, despite calls for them to be closed.

She added that genetic analysis of isolates from three patients suggests changes that might make the strain more pathogenic among birds, although that changes don't affect pathogenicity or transmissibility in humans.

Indeed, Shu told reporters that in the two such cases in mainland China, one patient has recovered and been released, while the other remains in hospital because of a chronic disease not related to the flu. (The third case was reported from Taiwan.)

The virus ordinarily does not cause disease among birds, making it difficult to track. In contrast, the H5N1 avian flu -- which first caused concern in 1997 -- is highly pathogenic to birds, causing widespread death in poultry flocks.

Other genetic changes seen in the current wave of human H7N9 flu include markers associated with resistance to some of the drugs used to treat influenza, Zhang said. The changes are in the neuraminidase protein, which might indicate resistance to oseltamivir (Tamiflu) and zanamivir (Relenza), which inhibit neuraminidase.

Shu added that the resistance markers for the most part have been seen in samples from patients after treatment, suggesting they are a result of therapy. Circulating viruses don't appear to be resistant, he said.

http://www.medpagetoday.com/InfectiousDisease/URItheFlu/63494

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WHO: H7N9 antiviral resistance likely arose after treatment

Officials from the World Health Organization (WHO) today revealed new information on antiviral resistance and other virus changes related to China's surge in H7N9 avian flu infections, but they said the shifts so far haven't changed the epidemiologic or clinical patterns of the disease in humans.

At a media telebriefing today, a WHO expert said that recently detected signs of resistance to antivirals like oseltamivir (Tamiflu) and zanamivir (Relenza) likely arose after treatment with antivirals in patients with H7N9. Experts added that the WHO is closely monitoring the H7N9 developments, as well as quickly changing events involving other avian flu strains with pandemic potential, such as the spread of highly pathogenic H5N8 to wild birds and poultry to 40 countries.

Two of the scientists who addressed journalists today are directors of WHO collaborating centers on influenza who are in Geneva this week attending meetings to guide the selection of seasonal flu strains for the Northern Hemisphere's 2017-18 flu season. The group will also look at the latest changes in potential pandemic strains, including H7N9, to assess if any new candidate vaccine viruses are needed.

Wenqing Zhang, MD, who leads the WHO's global influenza program, said the main message is that the risk of sustained human-to-human transmission is still low. "However, constant change is the nature of all influenza viruses, and that is why we follow the developments so closely," she said.

Antiviral resistance findings

So far, at least 460 H7N9 infections have been reported in China's fifth wave, its biggest yet, with the total number of cases reported since October accounting for one third of all cases since the novel virus was first detected in humans in 2013, Zhang said.

About 7% of the viruses from human cases in the fifth wave have genetic markers linked to resistance to neuraminidase inhibitors, including oseltamivir, the gold standard for treating the disease. She said the level is similar to earlier waves, with a slight elevation this season that is still lower than what health officials observed in the first wave.

Nearly all of the H7N9 viruses carrying the neuraminidase resistance marker have been from humans, suggesting that most of them developed the marker after treatment and weren't spread by poultry, Zhang said. She said none of the isolates from poultry had signs of neuraminidase inhibitor resistance and only one environmental sample showed the change. "WHO is closely monitoring these developments. So far there is no evidence to recommend changes in clinical management of infection."

Other changes, pandemic vaccine implications

She reiterated an earlier statement that the hemagglutinin mutation seen in three human samples and one environmental specimen involves changes that make the virus highly pathogenic in birds, but there is no evidence that they affect pathogenicity and transmissibility in humans.

Yuelong Shu, PhD, with the Chinese Center for Disease Control and Prevention (China CDC) and director of the WHO's collaborating center there, said one of two Guangdong province patients recently sickened by the virus containing the hemagglutinin mutation has been released from the hospital, and the other is still hospitalized for the treatment of an unrelated chronic condition. Taiwan this week reported that its patient found to be infected with the mutated strain, a 69-year-old man who was exposed to the virus in Guangdong province, has died.

Regarding other changes in the virus, Jackie Katz, PhD, who directs the WHO's collaborating center at the US Centers for Disease Control and Prevention said that, based on findings from multiple labs, H7N9 seems to have diverged two distinct genetic groups. Viruses in one of the groups are similar to candidate vaccine viruses that have been used to produce vaccine for the US Strategic National Stockpile.

At their meeting this week, the influenza experts are discussing the possible need to make additional H7N9 candidate vaccine viruses.

Virus sharing issues

Officials today responded to a report yesterday from Stat that China has not shared any virus isolates since shortly after it was first detected in humans, though they have frequently shared genetic sequences.

Katz said the delay in sharing isolates was linked to new regulations in China that shifted requests for samples from multiple groups to a commerce department outside of China CDC. She said a path forward has now been found to streamline the rapid sharing of viruses. Katz also commended China for rapidly sharing genetic sequences and epidemiologic information, which has been useful for developing timely risk assessments.

See also:

Mar 1 WHO media telebriefing audiofile

Feb 28 Stat story

http://www.cidrap.umn.edu/news-perspective/2017/03/who-h7n9-antiviral-resistance-likely-arose-after-treatment

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A patient with the H7N9 bird flu receiving treatment in a hospital in Wuhan, central China’s Hubei province, in February. Flu specialists from around the world met in Geneva this week to assess the global influenza situation. CreditAgence France-Presse — Getty Images

Although there has been a surge in human infections with H7N9 avian flu in China this winter, the risk of an epidemic remains low, a World Health Organization official said on Wednesday.

But the virus — which has killed about a third of the people known to have caught it — has now split into two distinct strains.

That will probably force development of a second small stockpile of emergency vaccine to be rolled out if the virus becomes more transmissible and threatens to turn into a pandemic, a scientist at the Centers for Disease Control and Prevention said.

Flu specialists from around the world gathered in Geneva this week to assess the global influenza situation and discuss with vaccine companies which viral strains should be in next winter’s flu shots.

China has had 460 lab-confirmed human cases of H7N9 bird flu this winter, said Dr. Wenqing Zhang, head of the W.H.O.’s global influenza program. That is the most in any flu season since the first human case was found in 2013.

The new strain kills more birds, which may make China’s poultry industry more willing to shut live bird markets and do more to protect poultry farms from infection.

Almost all cases have been caught directly from birds.

A few cases have been passed from a victim to a family member or caregiver, but there is no evidence of “sustained human-to-human transmission,” Dr. Zhang said.

Viruses designated H1, H2 or H3, along with a separate B lineage, have caused virtually all seasonal flu cases in humans. H5N1, a strain that sparked widespread fear of bird flu in 2003, still occasionally kills a few people each year, and another, H5N8, is widely circulating in poultry in Europe and the Middle East.

But no H5 or H7 strain has ever been transmitted easily among humans.

New cases of H7N9 are declining, so this winter’s outbreak appears to have peaked, said Yuelong Shu, an influenza expert at China’s Center for Disease Control and Prevention.

About 7 percent of the cases were resistant to drugs like Tamiflu. But that percentage, Dr. Shu added, has not increased substantially since 2013, and almost all resistant cases were in people who had already been treated with antivirals. Resistance probably arose individually in each patient, making it less likely that a drug-resistant strain is circulating in birds, he said.

As a precaution, American scientists have been making an H7N9 seed vaccine from which an emergency stockpile could be brewed if the virus became both lethal and highly transmissible, said Jacqueline Katz, deputy director of the C.D.C.’s flu division.

Now that the virus has split into two strains, the agency is discussing making a second seed vaccine, Dr. Katz said.

https://www.nytimes.com/2017/03/01/health/avian-flu-china-who.html?_r=0

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HEALTH

CDC Concerned by H7N9 Bird Flu’s Sudden Spread in China

A sudden surge in cases of H7N9 bird flu in China is a "cause for concern," the Centers for Disease Control and Prevention said Friday.

It's infected 460 people just since October, the CDC said in a report. "It's by far the largest epidemic wave since 2013," said CDC flu expert Dr. Tim Uyeki.

Image: Health officials in protective suits put a goose into a sack as part of preventive measures against the H7N9 bird flu at a poultry market in Zhuji
 
Health officials in protective suits put a goose into a sack as part of preventive measures against the H7N9 bird flu at a poultry market in Zhuji, Zhejiang province on Jan. 5, 2014. Reuters file

The CDC has been working on a vaccine against H7N9 just in case it's ever needed and is starting work on a second one now because it's started to mutate.

"It's a cause for concern, that's for sure," Uyeki told NBC News. "The surge in numbers of human H7N9 cases in China is definitely a concern."

The CDC issued a travel notice in January, cautioning travelers to China to stay away from live bird markets. Uyeki said travelers do not need to avoid China but they should be aware that poultry can spread the virus.

Related: WHO Says Watch Out for Bird Flu

Since 2013, H7N9 bird flu has infected 1,258 people, the CDC said. So 460 cases in just five months account for a third of all the cases over four years.

Earlier this week the World Health Organization held a meeting on H7N9 and then issued public reassurances, saying the virus did not appear to have changed in a way that would make it more likely to spread to people or to make it more dangerous to people.

Instead, the changes make the virus more dangerous to birds — which could be a good thing.

"These changes make the virus highly pathogenic in birds, meaning that it can cause some severe disease in birds," Dr. Wenqing Zhang, head of WHO's global influenza program, told reporters.

"Previously, H7N9 had only been observed to be 'low pathogenic' in birds, meaning the virus did not cause visible outbreaks of disease in birds," Zhang said.

If an avian influenza virus kills birds, it's bad for poultry farmers but it can give a warning that the virus is spreading. The problem with H7N9 has been that it does not make poultry sick, so it can spread among flocks without people knowing it.

a_30stk_bird_flu_150519.nbcnews-ux-1080-
 Can You Catch Bird Flu? 0:42

Uyeki is worried that H7N9 has become more widespread in China, spreading silently and infecting more people because it's infecting more birds.

"You could have more cases of human infection even if the risk of poultry-to-human transmission has not changed," he said.

China has been publishing genetic sequences of the H7N9 virus in public databases, but it has not been sharing actual samples of the virus, so it's not possible for U.S. labs to test the virus themselves to see whether it's changed and if so, whether it's more dangerous.

But it's already dangerous. H7N9 is considered a moderate to high pandemic threat, although the CDC and WHO do not think an H7N9 pandemic is about to happen, or even that it is certain to happen.

Related: CDC Issues H7N9 Travel Warning

H7N9 is one of several strains of bird flu that officials are watching because they have the potential to cause a human pandemic.

So far, H7N9 doesn't seem to infect people easily and people who are infected do not seem to spread it to others much. But influenza viruses change quickly and unpredictably, and if one starts passing easily from one person to another it could spread.

"From what we understand, there have been no real changes in the epidemiology or mortality of hospitalized H7N9 cases," Uyeki said.

H7N9 can be deadly when people do get it. It kills more than 40 percent of people who get sick enough to go to the hospital.

Related: H7N9 has cost billions

"Early symptoms are similar to those of seasonal flu and may include fever, cough, sore throat, muscle aches and fatigue, loss of appetite, and runny or stuffy nose," CDC said.

It often progresses to pneumonia. And hospitals or clinics treating people infected with H7N9 need to take precautions to make sure patients do not infect anyone else.

"Clinicians should consider the possibility of avian influenza A (H7N9) virus infection in people presenting with respiratory illness within 10 days of travel to China, particularly if the patient reports exposure to birds or poultry markets," the CDC says.

The CDC and WHO are watching the spread of several bird flu viruses that are known to infect people, including H5N1 and H7N2.

Related: Vet Catches Bird Flu From Cats

"Although the current risk to the public's health from A(H7N9) viruses is low, among the 12 novel influenza A viruses evaluated ... A(H7N9) viruses have the highest risk score and are characterized as posing moder­ate-high potential pandemic risk," the CDC team said in the report released Friday. 

http://www.nbcnews.com/health/health-news/cdc-concerned-h7n9-bird-flu-s-sudden-spread-china-n728946

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