Pandemic Influenza

Influenza is a highly contagious viral infection that causes annual flu epidemics in the United States and other countries. Each year in the United States, approximately 5 to 20 percent of the population contracts the flu; 1 more than 226,000 people are hospitalized; and 36,000 die from influenza infection or a secondary complication.2

  • Over time the influenza virus changes at a genetic level. This process, known as antigenic drift, leads to the different strains of flu that circulate among the human population. For this reason the make-up of the influenza vaccine is different every year.3
  • In contrast to gradual drift, the influenza virus can also change suddenly and dramatically. A genetic shift occurs when an animal virus gains the ability to infect humans or when human and animal viruses combine to create a new virus to which humans have little or no immunity. If a novel virus has the ability to spread easily from person to person and causes serious illness, then a pandemicI will almost always occur.4 A modern pandemic could lead to 200,000 to 2 million deaths in the United States.5
  • The novel H1N1 influenza strain currently circulating was declared a worldwide pandemic by the World Health Organization on June 11, 2009. This indicates that the virus was uncontained and being transmitted in communities in multiple parts of the world. Transmission has continued around the world and may increase in the Northern Hemisphere during fall and winter (flu season). Testing has shown that most people have little resistance to this strain, although those younger than 65 years of age appear to be at higher risk. A vaccination against novel H1N1 is currently being developed and is expected to be available by mid-October 2009. Much of the information in this fact sheet is based off predictions for different pandemic scenarios. Some or all of it will not pertain to the current novel H1N1 pandemic. For information concerning novel H1N1, see please refer to resources specific to it.6
  • A recent concern for a pandemic arises from the unprecedented outbreak of H5N1II avian influenza that has spread across bird populations in Asia, Europe Africa and the Near East. When it spreads from birds to humans it causes severe and often fatal disease. Most recently Europe has begun to see poultry outbreaks of H5N1.  Although the H5N1 strain currently does not have the ability to pass readily from one person to another, given enough opportunities there is a fear that the virus may mutate and become easily contagious.7
  • In the past century, three influenza pandemics have occurred.  The "Spanish Flu" pandemic of 1918 resulted in more than 50 million deaths worldwide. The 1957 "Asian Flu" and the 1968 "Hong Kong Flu" resulted in approximately 4 million deaths. All three were associated with high rates of morbidity and social disruption.8
  • The societal disruption of an influenza pandemic could be significant. Absenteeism across multiple sectors due to personal illness, illness among family members, fear of contagion, or public health measures to limit contact with others could threaten the functioning of critical infrastructure, the movement of goods and services, and operation of institutions such as schools. A pandemic would have significant implications for the economy, national security, and the basic functioning of society.9
  • The Centers for Disease Control and Prevention (CDC) estimates that in the United States a "medium–level" pandemic could cause 45 million outpatient visits, 865,000 hospitalizations, 209,000 deaths and a total of 90 million people being sick.10
  • Thirty percent or more of the general population are estimated to fall ill during an influenza pandemic and the economic impact of the outbreak could be as high as $768 billion in the US alone.11, 12
  • The Federal Government has already taken a series of actions, domestically and internationally, to address the pandemic threat. The National Strategy for Pandemic Influenza and its accompanying Implementation Plan are the basis of current efforts to prepare for and respond to a pandemic. 13
  • The goals of the Federal Government response to a pandemic are to:
    • Stop, slow and otherwise limit the spread of a pandemic to the United States.
    • Limit the domestic spread of a pandemic, and mitigate disease, suffering and death.
    • Sustain infrastructure and mitigate impact to the economy and the functioning of society.14
  • Vaccines and antiviral drugs could significantly reduce cases of illness and deaths during an influenza pandemic. While these medications can be stockpiled, an effective vaccine can only be made once the pandemic virus has been identified, a process that can take months. Researchers are developing a potential first-line vaccine for one strain of H5N1 and Federal officials have drafted a plan of who would be vaccinated first as high–risk groups in the case of a pandemic.15
  • Current research is striving for new antiviral medications that can reduce the severity of influenza and faster testing methods to aid in the monitoring, tracking, and quick treatment of outbreaks.16

Footnote:

I.  Pandemic – A pandemic occurs when a novel strain of influenza virus emerges and has the ability to infect and easily pass between humans. Because humans have little immunity to the new virus, a worldwide epidemic, or pandemic, can ensue.

II.  H5N1 - Avian influenza A H5 virus can be distinguished as "low pathogenic" and "high pathogenic" forms on the basis of genetic features of the virus and the severity of the illness it causes in poultry.



1 Centers for Disease Control and Prevention. Influenza Fact Sheet: Key Facts about Influenza and the Influenza Vaccine. March 12, 2009. Available at http://www.cdc.gov/flu/keyfacts.htm. Accessed on August 26, 2009.

2 Centers for Disease Control and Prevention. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. Morbidity and Mortality Weekly Report July 13, 2009;58[RR08]:1-52.

3 Center for Disease Control and Prevention. Avian Influenza: The Virus and Its Spread, Influenza Viruses. November 18, 2005. Available at http://www.cdc.gov/flu/avian/gen-info/flu-viruses.htm. Accessed on August 12, 2009.

4 Ibid.

5 Department of Health and Human Services. Pandemic Flu: Pandemic Planning Assumptions. August 26, 2009. Available at http://www.pandemicflu.gov/plan/pandplan.html  Accessed on August 26, 2009.

6 Centers for Disease Control and Prevention. Use of Influenza A (H1N1) 2009 Monovalent Vaccine: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. Morbidity and Mortality Weekly Report August 21, 2009;58[Early Release]:1-8.

7 Department of Health and Human Services. Pandemic Flu: General Information. August 26, 2009. Available at http://www.pandemicflu.gov/general/index.html/. Accessed on August 26, 2009.

8 Department of Health and Human Services. Pandemic Flu: Pandemics and Pandemic Threats Since 1900. August 26, 2009. Available at http://www.pandemicflu.gov/general/historicaloverview.html. Accessed August 26, 2009.

9 Department of Health and Human Services. Pandemic Flu: Pandemic Planning Assumptions. August 26, 2009. Available at http://www.pandemicflu.gov/plan/pandplan.html. Accessed on August 26, 2009.

10 Ibid.

11 Ibid.

12 Congressional Budget Office. A Potential Influenza Pandemic: An Update on Possible Macroeconomic Effects and Policy Issues. July 22, 2006. Available at http://www.cbo.gov/ftpdocs/72xx/doc7214/05-22-Avian%20Flu.pdf. Accessed on August 12, 2009.

13 Department of Health and Human Services. Pandemic Flu: Federal Planning and Response Activities. August 26, 2009. Available at http://www.pandemicflu.gov/plan/federal/index.html. Accessed on August 26, 2009.

14 Ibid.

15 Department of Health and Human Services. Pandemic Flu: Tests, Vaccines, Medications, and Masks. August 26, 2009. Available at http://www.pandemicflu.gov/vaccine/index.html. Accessed on August 26, 2009.

16 Ibid.