WHO RISK ASSESSMENT Human infections with influenza A(H7N9) virus 13April 2013

WHO RISK ASSESSMENT

Human infections with influenza A(H7N9) virus

13April 2013

Summary of available information
As of 13April 2013, a total of 49 confirmed cases of human infection with avian influenza A(H7N9)
virus have been reported to WHO by the China National Health and Family Planning Commission.
Among these cases, the ages range from 4 to 87; 15 are female. Eleven persons have died, and the
majority of the additional cases are considered severe. Of the 49 cases, 6 have been reported today
and further investigations are taking place. The cases have been reported from three provinces:
Anhui, Jiangsu and Zhejiang, and two municipalities, Beijing and Shanghai. All locations are in Eastern
and Northern China.
Two confirmed cases have been associated with possible family clusters, in which one and two
additional family members,respectively, developed severe pneumonia. Close contacts of confirmed
cases and health care workers caring for cases have been monitored for infection. So far, among the
contacts who have been tested by polymerase chain reaction, none has been shown to have
infection.
This is the first time human infection with this influenza subtype, avian influenza A(H7N9) virus, has
been detected. Previously,sporadic cases of human infection with otherinfluenza A(H7) viruses
have been reported. Those cases were associated with outbreaks of infection in poultry in other
countries. These earlierinfluenza A(H7) human infections generally resulted in mild influenza illness
with some conjunctivitis.
Genetic and laboratory characterization of the first three of these H7N9 virusesisolated from
humans indicatesthat:

• the virus contains a group of avian influenza virus genes from three different avian influenza
viruses;
• to date, genetic analyses of the isolates have shown certain changes, including amino acid
substitutions associated with increased affinity to alpha 2-6 receptors, which suggests that
the H7N9 virus may have greater ability to infect mammalian species, including humans,
than most other avian influenza viruses;
• there are sequence variations among the genes of three isolates that suggestthere has been
more than one introduction of this virus from animal into humans;
• these viruses are expected to be sensitive to the neuraminidase inhibitor drugs oseltamivir
and zanamivir, but resistant to the antiviral drugs amantadine and rimantadine;
• the isolates have a haemagglutinin structure thatis associated with low pathogenicity in
birds.
There are several gaps in critical information at this time, including the animal reservoir(s)in which
this virus is circulating, the main exposures and routes of transmission for how human infections
have been acquired, and the current scope of the spread of this virus among animal and human
populations. Avian influenza A(H7N9) viruses have now been isolated from poultry (including duck)
and pigeon in the live birdmarketsin some areas of China, but whether other potential reservoirs of

this virus may exist, including in other domestic and wild bird species, and mammalian species such
as pigs, has not yet been determined clearly.
So far, this virus has not been associated with reports of severe disease in poultry.
Risk assessment
This initial risk assessment, which has been prepared in accordance withWHO’s published
recommendations for rapid risk assessment of acute public health events1
will be updated as further
information becomes available.
What is the risk of the occurrence of further cases in the affected areas of China and other areas?
The epidemiology of this virus among animals, including the main reservoirs of infection among
animals and the extent of geographic spread, is not yet established. However, it is likely that most
human H7N9 infections so far are associated with infection among as-of-yet undetermined animals
and that further human cases of infection should be expected.
What is the risk of human-to-human transmission?

There is no evidence of sustained human-to-human transmission. However the two possible family
clusters suggestthat limited human-to-human transmissionmay occur where there is close contact
between cases and other individuals, as occurs in families and, potentially, healthcare settings.
Moreover, the genetic changes seen among these viruses suggesting adaptation to mammals is of
concern, and further adaptation may occur.
What isthe risk of international spread?
At this time, there is no information to indicate international spread of this virus. However, it is
possible that an infected person, who may or may not have symptoms, could travel to another
country. However, if the virus cannot sustain human-to-human transmission, as appears to be the
current situation, then extensive community spread is unlikely.
WHO does not advise special screening at points of entry with regard to this event, nor does it
recommend that any travel or trade restrictions be applied.


References
Most recent disease outbreak news can be found at:
http://www.who.int/csr/don/en/index.html
Background and summary of human infection with influenza A(H7N9) virus (as of 5 April 2013):
http://www.who.int/influenza/human_animal_interface/update_20130405/en/index.html
Frequently Asked Questions on human infection with influenza A(H7N9) virus, China:
http://www.who.int/influenza/human_animal_interface/faq_H7N9/en/index.html

Human infection with a new type of influenza virus A(H7N9)

The World Health Organization (WHO) has been officially notified by the China National Health and Family Planning Commission about human infection (and deaths) with an influenza virus subtype A(H7N9) that has not been previously reported in humans. There is no indication of human-to-human transmission associated with these patients. WHO is working closely with it's Collaborating Centres for influenza to discuss and strengthen diagnostics and case management. At present, the reservoir, source of infection and mode of transmission remain unknown.

Yellow fever vaccination booster not needed

17 MAY 2013 | GENEVA - The yellow fever ‘booster’ vaccination given ten years after the initial vaccination is not necessary, according to WHO. An article published in WHO’s Weekly Epidemiological Record (WER) reveals that the Organization’s Strategic Advisory Group of Experts on immunization (SAGE) has reviewed the latest evidence and concluded that a single dose of vaccination is sufficient to confer life-long immunity against yellow fever disease.

Since yellow fever vaccination began in the 1930s, only 12 known cases of yellow fever post-vaccination have been identified, after 600 million doses have been dispensed. Evidence showed that among this small number of “vaccine failures”, all cases developed the disease within five years of vaccination. This demonstrates that immunity does not decrease with time.

Important news for yellow fever endemic countries and travellers

“The conventional guidance has been that the yellow fever vaccination has had to be boosted after ten years,” says Dr Helen Rees, chair of SAGE. “Looking at really very good evidence, it was quite clear to SAGE that in fact a single dose of yellow fever vaccine is effective. This is extremely important for countries where yellow fever is endemic, because it will allow them to reconsider their vaccine scheduling. It is also important for travelers.”

Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes that is endemic to 44 countries in tropical areas of Africa and the Americas. Infection with the yellow fever virus causes varying degrees of disease, from mild symptoms to severe illness with bleeding and jaundice and fatal outcomes.

Estimated 200 000 new cases each year

There are an estimated 200 000 cases of yellow fever worldwide each year. About 15% of people infected with yellow fever progress to a severe form of the illness, and up to half of those will die, as there is no cure for yellow fever. The treatment is aimed simply at reducing patients’ discomfort.

The vast majority of reported cases and deaths occur in sub-Saharan Africa. In endemic regions of Africa, yellow fever natural immunity is acquired with age, putting children at highest risk of infection. Over the past two decades, the number of yellow fever cases worldwide has increased due to declining population immunity to infection, deforestation, urbanization, population movements and climate change.

Vaccination is the most effective measure

Vaccination is considered to be the most important and effective measure against yellow fever. Protective immunity develops within 30 days for 99% of people receiving the vaccination. For routine immunization programmes in Africa, home to 31 of the 44 yellow-fever endemic countries, the vaccine costs about $0.82 per dose.

SAGE is the principal advisory group to WHO for vaccines and immunization. It is charged with advising WHO on overall global policies and strategies, ranging from vaccines and technology, research and development, to delivery of immunization and its linkages with other health interventions. SAGE is concerned with all vaccine-preventable diseases including childhood vaccines and immunization.

For more information please contact:

Fadéla Chaib
Communications Officer/Spokesperson
Telephone: +41 22 791 32 28
Mobile: +41 79 475 55 56
E-mail: chaibf@who.int

Human infection with avian influenza A(H7N9) virus

17 MAY 2013 - Since 8 May 2013, no new laboratory-confirmed cases of human infection with avian influenza A(H7N9) have been reported to WHO by the National Health and Family Planning Commission, China. However, four additional deaths have been reported from previously laboratory-confirmed cases.

To date, WHO has been informed of a total of 131 laboratory-confirmed cases, including 36 deaths.

Authorities in affected locations continue to maintain enhanced surveillance, epidemiological investigations, close contact tracing, clinical management, laboratory testing and sharing of samples as well as prevention and control measures. In the past week, the Shanghai and Zhejiang provincial governments have started to normalize their emergency operations into their routine surveillance and response activities. WHO offices in country, regional and headquarters continue to work closely to ensure timely information updates.

Until the source of infection has been identified and controlled, it is expected that there will be further cases of human infection with the virus.

So far, there is no evidence of sustained human-to-human transmission.

WHO does not advise special screening at points of entry with regard to this event, nor does it currently recommend any travel or trade restrictions.

WHO continues to work with Member States and international partners. WHO will provide updates as the situation evolves.