- Texas Medical Center. Pandemic Influenza Preparedness and Response Guide. November 2011. The State of Texas. Pandemic Influenza Response, Appendix 7 to Annex H. March 2007.
- The University of Texas at Austin. Infectious Disease Plan Annex. January 2011.
- United States Department of Health and Human Services and The Centers for Disease Control and Prevention. Interim Pre-pandemic Planning Guidance: Community Strategy for Pandemic Influenza Mitigation in the United States, Appendix 7 - Pandemic Influenza Community Mitigation Interim Planning Guide for Colleges and Universities. February 2007.
- United States Department of Health and Human Services and The Centers for Disease Control and Prevention. Preparing for the Flu (Including 2009 H1N1 Flu) A Communication Toolkit for Institutions of Higher Education.
- Center for Disease Control and Prevention: Coronavirus Disease 2019 (COVID-19)
According to the Centers for Disease Control and Prevention (CDC), pandemic influenza occurs when a new influenza A virus emerges for which there is little or no immunity in the human population. The virus then begins to cause serious illness and then spreads easily person-to-person worldwide. Characteristics of a pandemic influenza include rapid worldwide spread, overwhelming of healthcare systems, inadequate medical supplies, and economic and social disruption.
National and federal organizations have classified stages of pandemic influenza to better formulate guidance based on the impact of the virus. This section of the guide details these classifications.
World Health Organization
The World Health Organization (WHO) has developed a method for classifying the rate of worldwide transmission of an influenza virus. This method, known as the WHO pandemic phases1, identifies six phases of an influenza pandemic across three pandemic periods.
- Phase 1: No new influenza virus subtypes have been detected in humans. No viruses circulating among animals have been reported to cause infections in humans.
- Phase 2: No new influenza virus subtypes have been detected in humans. However, an animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered a potential pandemic risk.
Pandemic Alert Period
- Phase 3: An animal or human-animal influenza re-assortment virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. Limited human-to-human transmission may occur under some circumstances (for example, when there is close contact between an infected person and an unprotected caregiver). However, limited transmission under such restricted circumstances does not indicate that the virus has gained the level of transmissibility among humans necessary to cause a pandemic.
- Phase 4: There is verified human-to-human transmission of an animal or human-animal influenza re-assortment virus able to cause community-level outbreaks, but is generally seen in small clusters. The ability to cause sustained disease outbreaks in a community marks a significant upward shift in the risk for a pandemic. Any country that suspects or has verified such an event is encouraged to consult with the WHO so that the situation can be jointly assessed and a decision made by the affected country if implementation of a rapid pandemic containment operation is warranted. Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a foregone conclusion.
- Phase 5: There are larger clusters but human-to-human spread is still localized, suggesting that the virus is becoming increasingly adapted to humans but may not yet be fully transmissible(substantial pandemic risk). While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.
- Phase 6: There is increased and sustained transmission in the general population in multiple countries.
United States Government
The Department of Health and Human Services and CDC work closely to plan for, respond to, and recover from emerging disease outbreaks, including pandemic influenza. While these efforts are constantly evolving, the national strategy is based on three (3) pillars2:
- Preparedness and Communication: Activities that should be undertaken before a pandemic to ensure preparedness and the communication of roles and responsibilities to all levels of government, segments of society, and individuals.
- Surveillance and Detection: Domestic and international systems that provide continuous situational awareness to ensure the earliest warning possible to protect the population.
- Response and Containment: Actions to limit the spread of the outbreak and to minimize the health, social, and economic impacts of a pandemic.