The pandemic influenza phases reflect WHO’s risk assessment of the global situation regarding each influenza virus with pandemic potential that is infecting humans. These assessments are made initially when such viruses are identified and are updated based on evolving virological, epidemiological and clinical data. The phases provide a high-level, global view of the evolving picture.
The global phases – interpandemic, alert, pandemic and transition – describe the spread of the new influenza subtype, taking account of the disease it causes, around the world. As pandemic viruses emerge, countries and regions face different risks at different times. For that reason, countries are strongly advised to develop their own national risk assessments based on local circumstances, taking into consideration the information provided by the global assessments produced by WHO. Risk management decisions by countries are therefore expected to be informed by global risk assessments, but based on local risk assessments.
The risk-based approach to pandemic influenza phases is represented in Figure 1 as a continuum, which also shows the phases in the context of preparedness, response and recovery, as part of an all-hazards approach to emergency risk management. Both WHO guidance and international standards exist that describe formats and conduct of such risk assessment (see Section 4.2). One of the underlying principles of this guidance is to acknowledge that emergency risk management at country level needs to be sufficiently flexible to accommodate different consequences within individual countries, for example, different severities and different numbers of waves of illness.
The global phases will be used by WHO to communicate the global situation. They will be incorporated into IHR (2005) related communications to National IHR Focal Points, in Disease Outbreak News releases and various other public and media interactions, including through social media channels.
Alert phase: This is the phase when influenza caused by a new subtype has been identified in humans.5 Increased vigilance and careful risk assessment, at local, national and global levels, are characteristic of this phase. If the risk assessments indicate that the new virus is not developing into a pandemic strain, a de-escalation of activities towards those in the interpandemic phase may occur.
Pandemic phase: This is the period of global spread of human influenza caused by a new subtype. Movement between the interpandemic, alert and pandemic phases may occur quickly or gradually as indicated by the global risk assessment, principally based on virological, epidemiological and clinical data.
Transition phase: As the assessed global risk reduces, de-escalation of global actions may occur, and reduction in response activities or movement towards recovery actions by countries may be appropriate, according to their own risk assessments.
The global phases and their application in risk management are distinct from (1) the determination of a PHEIC under the IHR (2005) and (2) the declaration of a pandemic. These are based upon specific assessments and can be used for communication of the need for collective global action, or by regulatory bodies and/or for legal or contractual agreements, should they be based on a determination of a PHEIC or on a pandemic declaration.
Determination of a PHEIC: The responsibility of determining a PHEIC lies with the WHO Director-General under Article 12 of the IHR (2005). The determination leads to the communication of temporary recommendations, see Section 2.1.
Declaration of a pandemic: During the period of spread of human influenza caused by a new subtype, and appropriate to the situation, the WHO Director-General may make a declaration of a pandemic.
While the determination of a PHEIC and/or declaration of a pandemic may trigger certain regulatory actions by WHO and Member States, actions at national level should be based on national/local risk assessments and be commensurate with risk.
Actions by WHO occur throughout the phases continuum; their nature and scale at any point in time will be in line with the global risk assessment. Indicative actions by the Organization are illustrated in Figure 2. For further examples of WHO actions, see Section 3.2.
National actions: The nature and scale of national actions at any point in time will be in line with the current national risk assessments, taking into consideration the global risk assessment. The uncoupling of national actions from global phases is necessary since the global risk assessment, by definition, will not represent the situation in individual Member States. For further information on suggested national actions, see Section 5.
Link to the Pandemic Influenza Risk Management- WHO Interim Guidance- June 2013 http://www.who.int/influenza/preparedness/pandemic/influenza_risk_management/en/