(CNN)Here's a look at the H1N1 influenza virus, also known as swine flu. There was a pandemic outbreak across the globe which lasted from 2009 to 2010.
Human cases of H1N1 from April 2009-April 2010
Fatalities in the United States - Estimated total is 12,469.
Fatalities Worldwide - A 2012 study estimated a range between 151,700 and 575,400 deaths.
Swine flu is a respiratory disease caused by type A influenza virus in pigs. Swine flu outbreaks are common in pig herds, but generally the disease causes few deaths in pigs.
Swine flu is transmitted between pigs through close contact and contact with contaminated objects. Flu spreads when someone touches an object coughed or sneezed on by an infected person and then touches his/her mouth or nose. However, swine flu cannot be passed from properly handled pork products to humans.
Swine flu outbreaks in pigs can occur at any time, but mostly occur during the late fall and winter months.
It is a constantly mutating virus. Pigs are susceptible to viruses from birds, humans and other swine. When different influenza viruses strike pigs, the genes can mutate and new viruses can develop.
In pigs, there are currently three common influenza A virus subtypes in the United States: H1N1, H1N2 and H3N2.
Swine Flu in Humans
Swine flu occurs in people that are in contact with infected pigs. When this occurs, it is called a "variant influenza virus."
Symptoms are similar to that of regular human influenza and can include fever, lethargy, lack of appetite, coughing, runny nose, sore throat, nausea, vomiting and diarrhea.
Antiviral drugs that treat variant flu infections in humans are oseltamivir (Tamiflu), zanamivir (Relenza) and peramivir (Rapivab).
1930 - The swine flu virus (an influenza type A H1N1 virus) is first isolated from a pig.
1976 - Swine flu (Hsw1N1) breaks out among soldiers at Fort Dix in New Jersey. At least four soldiers are infected and one dies.
1976 - The United States begins a nationwide vaccination program against a type of swine flu known as Influenza A/New Jersey/76. However, the program is suspended after people who received shots develop a rare illness called Guillain-Barré syndrome.
September 1988 - A woman dies of the H1N1 flu virus days after visiting a county fair pig exhibition where there was widespread influenza-like illness among the swine.
December 2005-February 2009 - The Centers for Disease Control and Prevention reports 12 cases of swine flu among humans.
April 2009 - Swine influenza A (H1N1) virus is detected in a 10-year-old boy. CDC lab testing confirms the same virus in a second California child residing about 130 miles away from the first patient.
April 24, 2009 - The CDC issues an outbreak notice warning travelers of an increased health risk of swine flu in Central Mexico and Mexico City.
April 26, 2009 - The United States declares a public health emergency as cases of swine flu increase.
April 27, 2009 - World Health Organization (WHO) raises the influenza pandemic alert to a level 4, which means that there has been human-to-human transmission of the virus.
April 29, 2009 - WHO raises the influenza pandemic alert to a level 5, indicating sustained community-level outbreaks in two or more countries within the same region.
June 11, 2009 - WHO raises the influenza pandemic alert to a level 6. The outbreak is now being considered a global pandemic.
October 24, 2009 - US President Barack Obama declares the H1N1 outbreak a national emergency.
August 10, 2010 - WHO Director General Dr. Margaret Chan announces that the H1N1 outbreak has moved into the post-pandemic period.
June 26, 2012 - A study published in the Lancet Infectious Diseases journal estimates that the global death toll from the pandemic ranges between 151,700 and 575,400.