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Influenza Pandemics
THE SIX STAGES AND THREE PERIODS OF PANDEMICS
In its Global Influenza Preparedness Plan, 5/2005, the World Health Organization (WHO) defines three pandemic periods comprising of six phases (click image to enlarge):
The Pandemic Periods and there phases:
− the interpandemic period (phases 1 and 2)
− the pandemic alert period (phases 3, 4 and 5)
− the pandemic period (phase 6).
Phases 1 to 6 cover the course of the pandemic from the time a new influenza virus subtype (such as H5N1) emerges in animals until the disease has spread to infect people worldwide.
Each phase is declared by the WHO as soon as the corresponding criteria have been met. The WHO member states are expected to activate the relevant phase of their influenza pandemic plans when a phase is declared by the WHO.
Interpandemic period - Phase 1
Description: No new influenza virus subtypes have been detected in humans anywhere in the world.
Objective: To periodically adapt pandemic plans and preparations to new findings at the global, national and regional levels.
Strategy: In this situation, the emphasis is on ensuring that risk groups and medical and nursing personnel receive seasonal influenza vaccinations.
Interpandemic period - Phase 2
Description: Like Phase 1. However, a new influenza virus subtype circulating in animals is presenting a substantial risk of illness to humans.
Objective: To keep the risk of the disease being transmitted from animals to humans as low as possible; any cases of transmission are discovered and notified immediately.
Strategy: As in Phase 1 plus additional emphasis is placed on preventing the introduction of the new influenza virus subtype (e.g. H5N1) to the at-risk animal population and on avoiding infection in exposed individuals, e.g. those working in the control of animal epidemics.
Pandemic alert period - Phase 3 (Our current Phase)
Description: There are isolated cases of humans being infected with a new influenza virus subtype. However, there is no human-to-human transmission. There may be rare exceptions involving individuals who live or work in close contact with animals1 (e.g. infected poultry).
Objective: To ensure rapid characterization of the new influenza virus subtype, early detection and notification, and an early response to additional human cases.
Strategy: If it is not possible to prevent the introduction of the new virus subtype (e.g. H5N1) to the animal population, the virus must be eliminated and the infection of exposed individuals must be prevented. Human infections which occur nonetheless must be identified as early as possible. Appropriate contact management will then be necessary. A strategy for provision of antiviral drugs and vaccines must be developed and reviewed and the supply of drugs must be ensured in preparation for the following phases.
Pandemic alert period - Phase 4
Description: There are small outbreaks of the infection with the first cases of human-to-human transmission. Spread is highly localized, suggesting that the virus is not yet adapted very extensively to humans.
Objective: To contain the new influenza virus subtype (e.g. H5N1) or at least delay its spread to gain time to implement preparedness measures, including procurement of a vaccine.
Strategy: The emphasis is on preventing the new influenza virus subtype (e.g. H5N1) from being brought into the country by humans or animals. If this is not successful, an effort must be made to interrupt the animal-to-human and human-to-human chains of transmission.
Possible impact: In this situation, cross-border traffic may be restricted, e.g. air travel from the affected region as travellers returning to their nation may pose a threat. The organization of international events may be jeopardized (as was the case with SARS, for example); large numbers of nationals living abroad may return home. Each nation will try to prevent the disease from entering the country. They will identify infected individuals entering the country at an early stage in order to contain the virus or slow its spread.
This situation may constitute an emergency. Medical personnel may be heavily burdened and in some instances overwhelmed. Non-medical fields such as business, the diplomatic service and security may be heavily affected.
Pandemic alert period - Phase 5
Description: Larger clusters but still localized, suggesting the virus is becoming increasingly adapted to humans. However, the virus is not yet fully transmissible.
Objective: To maximize efforts to contain or delay the spread of the new influenza virus subtype (e.g. H5N1) in order to avert a pandemic and to gain time for response measures.
Strategy: As in Phase 4.
Pandemic period - Phase 6
Description: Widespread, sustained transmission of the new influenza virus subtype which has developed into a pandemic virus.
Objective: To minimize the impact of the pandemic.
Strategy: Social and economic activities must continue as normally as possible.
Scenario: The precise strategy and the extent of the measures that need to be taken in the scenarios for Phase 6 will be determined to a large extent by how lethal the pandemic virus is. For example, if a pandemic virus is spreading persistently and globally from human to human there is an urgent need for a pandemic vaccine.
Also, the burden on the healthcare system will be many times greater than during an outbreak of seasonal flu; the healthcare system may be overwhelmed. All aspects of life and society are also seriously affected. The crisis situation may lead to unrest in the population, the development of black markets, and outbreaks of violence.
References
CDC, USA. Prevention and control of influenza: Recommendations of the
Advisory Committee on Immunization Practices (ACIP). MMWR (Morbidity and
mortality weekly report) 2005; 54(RR-08): 1-40.
http://www.cdc.gov/flu/professionals/background.htm
Commission of the European Communities. Pandemic Influenza Preparedness and
Response Planning in the European Community. Brussels, 28.11.2005. COM(2005)
607 final.
Federal Office of Public Health (FOPH),
www.bag.admin.ch Swiss Influenza Pandemic Plan, page 66 of 251
Poll results:
Our Quick Poll for September asked
"Which Avian Flu early warning system would you prefer if available?"
E-mail? 33.3 %
SMS? 8.3%
TV / Radio? 33.3%
Other? 25%
These percentages were from some 800 votes from various countries.
Next: » The Ethics of Pandemics - who gets the medicine and who decides
All Articles
in this series:
» The Influenza Pandemics of the 20th Century.
» Defending ourselves against the next influenza
pandemic.
» Outcomes and Social Reshaping following a 21st Century Pandemic.
» The six phases and three periods defined by WHO for Pandemics.
» The Ethics of Pandemics - who gets the medicine and who decides.
» Scenario - how the next influenza pandemic is likely to start.
Video Presentation:
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The Affects of Bird Flu on Business - First Business Morning News. A
good overview of what is and needs to be done. (Opens in a new window on the
Google Video site.)