An influenza pandemic is a global outbreak of disease that occurs when a new influenza virus appears or “emerges” in the human population, causes illness, and then spreads easily from person to person worldwide. Pandemics are different from seasonal outbreaks or “epidemics” of influenza. Seasonal outbreaks are caused by subtypes of influenza viruses that already circulate among people, whereas pandemic outbreaks are caused by new subtypes, by subtypes that have never circulated among people, or by subtypes that have not circulated among people for a long time. Past influenza pandemics have led to high levels of illness, death, social disruption, and economic loss.
H5N1 Influenza (Avian Flu)
An outbreak of highly pathogenic avian influenza caused by a strain of H5N1 avian influenza started in Asia in the fall of 2003 and quickly spread in domestic poultry farms. In the summer of 2005, H5N1 began expanding its geographic range beyond Asia. This trend has continued, and human cases of the H5N1 avian influenza have now been reported in 15 countries in Asia, Europe and Africa. This strain of influenza is highly pathogenic, meaning it can cause severe illness and death.
Almost all cases of H5N1 avian influenza have been caused by direct contact with sick birds. The virus does not spread easily from person-to-person. However, flu viruses are constantly changing. No one knows for sure whether H5N1 avian influenza will become easily transmissible from human-to-human, or if it will cause an influenza pandemic . But scientists and government officials believe it could pose a serious threat to our health. It’s something that we all need to take seriously and plan for.
2009 H1N1 Influenza (Swine Flu)
2009 H1N1 Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza viruses that cause regular outbreaks in pigs. People do not normally get swine flu, but human infections can and do happen. In spring of 2009, a new form of the Influenza A virus was found to be causing disease and death in Mexico. The new virus, now called the 2009 H1N1 virus, contains genetic components from avian influenza, swine influenza and human influenza.
The symptoms of the 2009 H1N1 flu in people are similar to the symptoms of regular seasonal influenza and include fever, cough, sore throat, body aches, headaches, chills and fatigue. The vast majority of 2009 H1N1 cases have been mild to moderate illness, and the patients recovered. However, there has been serious illness and deaths associated with this virus, particularly in people with underlying health conditions. Like seasonal flu, H1N1 flu may cause a worsening of underlying chronic medical conditions.
The 2009 H1N1 influenza spread rapidly around the world. On June 11, 2009 the World Health Organization (WHO) raised the worldwide pandemic alert level to Phase 6 in response to the ongoing global spread of the 2009 H1N1 virus. A Phase 6 designation indicates that a global pandemic is underway. It is important to understand that the term “pandemic” refers to the spread of a disease, not the severity. The pandemic alert level stayed at Phase 6 until August 10, 2010, when the World Health Organization declared the pandemic to be over. For more information on the 2009 H1N1 Pandemic go to http://www.cdc.gov/h1n1flu/cdcresponse.htm.
The 2009 H1N1 virus is still circulating, along with seasonal flu viruses, in many parts of the world, and will probably continue to do so for years to come. The U.S. 2010-2011 seasonal influenza vaccine will protect against the 2009 H1N1 virus, as well as an H3N2 virus, and an influenza B virus.