pandemic influenza




Influenza (“flu”) is a respiratory illness that can be transmitted from person to person. Flu viruses are of two main genetic types: Influenza A and B. Influenza A strains are further identified by two important surface proteins that are responsible for virulence: hemagglutinin (H) and neuraminidase (N).

Seasonal flu circulates each year in the winter in each hemisphere. The dominant flu strains in global circulation change from year to year, but most people have some immunity; infection can be fatal. CDC estimates that there are about 36,000 deaths from seasonal flu each year, on average. Vaccines are made each year based on predictions of the strains that are most likely to circulate in the upcoming flu season.

Avian flu (“bird flu”) is caused by viruses that occur naturally among wild birds, and that may also affect domestic poultry. In 1997 a new H5N1 strain of avian flu emerged in Asia, and has since caused millions of deaths among domestic poultry, and hundreds of deaths in humans. Health officials have been concerned that this strain could cause a human pandemic, and governments around the world have carried out a number of preparedness activities, including vaccine development and stockpiling, and planning for continuity of services.

Swine flu occurs naturally and may cause outbreaks among wild and domestic swine. People do not normally get swine flu, but each year CDC identifies a few isolated cases of human flu that are caused by flu strains typically associated with swine.

Pandemic flu is caused when a novel strain of human flu (i.e., one that spreads from person to person) emerges and causes a global outbreak, or pandemic, of serious illness. Because there is little natural immunity, the disease is often more severe than is typical of seasonal flu. (Adapted from HHS, “Flu Terms Defined,” For more information about pandemic flu, see “Understanding Pandemic Influenza” in CRS Report RL33145, Pandemic Influenza: Domestic Preparedness Efforts.)

To address the threat, the Obama Administration has requested more than $4 billion in emergency supplemental appropriations, and has asked for budget transfer authorities to mobilize additional amounts. Funds were also requested in regular FY2010 appropriations. House and Senate appropriators have included pandemic flu funding in pending FY2009 supplemental appropriations legislation. Congressional committees in both chambers have convened hearings to assess the situation.

Efforts to prepare for a possible mass vaccination campaign are underway, including development of and clinical trials on a prototype vaccine, and limited mass production of pilot lots. Federal officials note that a decision to actually administer vaccine broadly across the population would be made separately, based on circumstances in the future.

Key Official Actions by WHO

Determination of Influenza Pandemic Phase

The World Health Organization is the coordinating authority for health within the United Nations system. It is responsible for providing leadership, guiding a research agenda, setting norms and standards, articulating evidence-based policy options, providing technical support to countries, and monitoring and assessing health trends. WHO does not have enforcement powers.

An influenza pandemic occurs when a novel flu strain emerges and spreads across the globe, causing human illnesses. For that to happen, the virus must have the following features: it must be genetically novel so that there is a lack of preexisting immunity; it must be pathogenic (i.e., capable of causing illness in humans); and it must be easily transmitted from person to person.

WHO, in consultation with experts in member countries, monitors the spread of influenza among human populations, and has developed a scale to monitor pandemic risk. It consists of five “prepandemic” phases with increasing incidence of animal and then human illness and transmission, and a sixth phase that represents a full-blown human pandemic, with sustained viral transmission and outbreaks in most or all regions of the world. Historically, flu pandemics have occurred in multiple waves before subsiding.

As a result of the rapid spread of the new flu strain, WHO raised the pandemic alert level from Phase 3, where it had been for several years because of the threat of H5N1 avian flu, to Phase 4 on April 27, and then to Phase 5 on April 29.3 Phase 3 meant that a novel flu strain was causing sporadic small clusters of human illness, but was not sufficiently transmissible to sustain community-level outbreaks. Phase 4, by contrast, signaled that human-to-human transmission of the new H1N1 virus was sufficient to sustain community-level outbreaks. According to WHO, raising the alert level to Phase 5 meant that there was sustained community-level transmission in two or more countries within one WHO region, and that a pandemic could be imminent.

On June 11, WHO raised the level to Phase 6, declaring that an influenza pandemic, caused by the new H1N1 strain, was underway.5 According to WHO Director General Dr. Margaret Chan:

Spread in several countries can no longer be traced to clearly-defined chains of human-tohuman transmission. Further spread is considered inevitable.... The world is now at the start of the 2009 influenza pandemic. We are in the earliest days of the pandemic. The virus is spreading under a close and careful watch. No previous pandemic has been detected so early or watched so closely, in real-time, right at the very beginning. The world can now reap the benefits of investments, over the last five years, in pandemic preparedness.

WHO Influenza Pandemic Phases
(current alert level is highlighted)

Phase 1
No animal influenza virus circulating among animals has been reported to cause infection in humans.

Phase 2
An animal influenza virus circulating in domesticated or wild animals is known to have caused infection in humans and is therefore considered a specific potential pandemic threat.

Phase 3
An animal or human-animal influenza reassortanta virus has caused sporadic cases of small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks.

Phase 4
Human-to-human transmission of an animal or human-animal influenza reassortant a virus able to sustain community-level outbreaks has been verified.

Phase 5
The same identified virus has caused sustained community-level outbreaks in two or more countries in one WHO region.b

Phase 6
An influenza pandemic. In addition to the criteria defined in Phase 5, the same virus has caused sustained community-level outbreaks in at least one other country in another WHO region.b

Post-peak Period
Levels of pandemic influenza in most countries with adequate surveillance have dropped below peak levels.

Possible New Wave
Level of pandemic influenza activity in most countries with adequate surveillance rising again.

Post-pandemic Period
Levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance.

Source: Adapted from WHO, Pandemic Influenza Preparedness and Response:
A WHO Guidance Document, April 2009,

a. A reassortant virus results from a genetic reassortment process in which genes from animal and human influenza viruses mix together to create a new strain.

b. WHO governs through six regional offices that do not strictly correspond with the world’s continents. The WHO regions are the African Region; the Region of the Americas; the South-East Asia Region; the European Region; the Eastern Mediterranean Region; and the Western Pacific Region. See “WHO–Its People and Offices,”

Source :
The 2009 Influenza Pandemic: An Overview
Sarah A. Lister Specialist in Public Health and Epidemiology
C. Stephen Redhead Specialist in Health Policy
June 12, 2009

What is swine influenza?
Influenza Defined
Influenza Viruses - Types, Subtypes, and Strains
What is pandemic influenza A(H1N1) 2009 virus?
Definitions for identification of pandemic influenza A(H1N1) 2009
Case Management & Infection Control
Who should be tested?
Step-by-step guide for specimen collection, storage and transportation
Doctors/Nurses directions to Patients/Parents
How Influenza Viruses Change: Drift and Shift
The 2009 Influenza Pandemic
International Health Regulations
Vaccine Development and Use
Naming the Virus Strain
Information for Families and Visitors
New Pandemic Influenza A (H1N1) 2009
Pandemic (H1N1) 2009 Influenza Guidance
Recent Results from Studies with the new 2009 A/H1N1 Influenza A Virus
Continued pandemic influenza virus detections across Europe with increased activity in the UK (Northern Ireland)
Highly Pathogenic Avian Influenza Virus H5N1 and Wild Birds



The Clean Development Mechanism global warming Reducing emissions (REDD)
heart attack influenza Cholesterol