Flu Pandemic


A flu pandemic, also called an influenza pandemic, is an epidemic caused by an influenza virus, which covers a major portion of the world and infects a large proportion of humans. Though a flu pandemic occurs only infrequently, when one does occur it can cause many deaths. For instance, the 1918–1919 Spanish flu pandemic caused 20 to 50 million people to die.


The Spanish flu outbreak was not especially lethal in terms of number of deaths per total cases (by 1918 standards; however, the virus infected at least an estimated 500 million people). It was, however, very lethal to otherwise healthy adults ages twenty to forty-four years, as opposed to most flu outbreaks, which kill only the very young, the elderly, and people with weakened immune systems. Scientists and public health officials continue to study Spanish flu in the hopes of preventing a similar outbreak.

The Spanish flu virus caused one of the worst infectious disease pandemics ever recorded in modern history. Although the threats of some diseases, such as smallpox, have been contained by vaccination programs, influenza remains a difficult disease. There are worldwide outbreaks of influenza every year (approximately 300,000–500,000 people die of influenza or influenza complications each year—about 36,000 in the United States alone), and the flu typically reaches pandemic proportions (lethally afflicting an unusually high portion of the population) every ten to forty years. Prior to the declaration of a global pandemic of 2009 A H1N1 influenza in June 2009, the last influenza pandemic was the Hong Kong flu of 1968–1969, which caused an estimated one million deaths worldwide and killed approximately 33,000 Americans.

Weekly influenza report. Percentage of visits for influenza-like illness (ILI) reported, 2016–2017.

Weekly influenza report. Percentage of visits for influenza-like illness (ILI) reported, 2016–2017.
Risk factors

The influenza virus is highly mutable, so each year's flu outbreak presents the human body with a slightly different virus. Because of this, people do not build immunity to influenza. Vaccines are successful in protecting people against influenza, but vaccine manufacturers must prepare a new batch each year, based on their best supposition (hypothesis) of which particular virus will spread.


Most influenza viruses originate in Asia. Therefore, doctors, scientists, and public health officials closely monitor flu cases there to make the appropriate vaccine. The two main organizations tracking influenza are the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). The CDC and other government agencies had been preparing for a flu pandemic on the level of Spanish flu since the early 1990s.

Causes and symptoms

Various symptoms are present with influenza. They include body aches, chills, cough, fatigue, fever, headache, runny or stuffy nose, and sore throat. A medical professional can prescribe antiviral drugs to treat these symptoms. Scientists are researching the causes of the various flu pandemics that have occurred on Earth. Two highly researched pandemics are the Spanish influenza and the 2009 A H1N1 influenza.

Spanish influenza

Seattle police wearing protective masks during the influenza pandemic of 1918–19, in which 20 million people died. Historical and epidemiological data are inadequate to identify the geographic origin.

Seattle police wearing protective masks during the influenza pandemic of 1918–19, in which 20 million people died. Historical and epidemiological data are inadequate to identify the geographic origin. Most victims were healthy young adults, unlike most influenza outbreaks, that affect juvenile, elderly, or weakened patients.
(Science History Images / Alamy Stock Photo)

Named the Spanish Flu because it was incorrectly believed to have originated in Spain, this horrible strain of influenza was a global epidemic, affecting World War I soldiers as well as civilians. Because this epidemic began during World War I, it spread quickly throughout the world as soldiers and ships moved from country to country. In 1919, President Woodrow Wilson even contracted the disease while negotiating the Treaty of Versailles. The classic flu symptoms quickly progressed to pneumonia, extremely high fevers, and cyanosis. It is now believed that the Spanish Flu actually began in the United States.

Usually influenza has dire consequences for infants and the elderly. Surprisingly, the Spanish Flu's death rate was much higher in young adults. Of the total number of Spanish Flu-related deaths in 1918–1919, 99% of them were people 65 or younger.

The Spanish Flu killed approximately 50 million people worldwide, causing more deaths than the World War. It has been termed “the greatest medical holocaust in history.” Many experts warn that another influenza-based epidemic could be on the horizon, and recent cases of Avian Influenza have shown similiarities in the genetic code. Scientists are using tissue samples from the 1918 victims to research and develop vaccines and treatment plans in preparation for another worldwide epidemic.

Social conditions at the time probably contributed to the remarkable power of the disease. The flu struck just at the end of World War I, when thousands of soldiers were moving from America to Europe and across that continent. In a peaceful time, sick people may have gone home to bed, and thus passed the disease only to their immediate family. However, in 1918, men with the virus were packed in already crowded hospitals and troop ships. The unrest and devastation left by the war probably hastened the spread of Spanish flu. So it is possible that if a similarly virulent virus were to arise again soon, especially with modern anti-viral medicines, it would not be as deadly.

Researchers are concerned about a return of Spanish flu because little is known about what made it so virulent. The flu virus was not isolated until 1933, and since then there have been several efforts to collect and study the 1918 virus by exhuming corpses in Alaska and Norway, where bodies were preserved in permanently frozen ground. In 1997, a Canadian researcher, Kirsty Duncan (1966–), was able to extract tissue samples from the corpses of seven miners who had died of Spanish flu in October 1918 and were buried in frozen ground on a tiny island off Norway. Duncan's work allowed scientists at several laboratories around the world to do genetic work on the Spanish flu virus. It was subsequently determined by researchers that the Spanish flu was a mixture of genes, including avian genes.

2009 A H1N1 influenza

The 2009 pandemic H1N1 virus proved to be less lethal than many other flu viruses (for example it is not as lethal as the H5N1, Spanish, or Hong Kong viruses), and infectious disease experts predicted that the 2009 influenza pandemic would not approach the severity of prior pandemics such as the 1918–1919 Spanish flu. Priorities for responding to the pandemic included manufacturing and delivering sufficient quantities of antiviral drugs and vaccine specific to the 2009 H1N1 virus.


The influenza virus is believed to originate in migratory waterfowl, particularly ducks. Ducks carry influenza viruses without becoming ill. They excrete the virus in their feces. When their feces collect in water, other animals can become infected. Domestic turkeys and chickens can easily become infected with influenza virus borne by wild ducks. However, most avian (bird-borne) influenza does not pass to humans, or if it does, is not particularly virulent. Other mammals, too, can pick up influenza from either wild birds or domestic fowl. Whales, seals, ferrets, horses, and pigs are all susceptible to bird-borne viruses. When the virus moves between species, it may mutate. Human influenza viruses may sometimes pass from ducks to pigs to humans.

A flu outbreak among chickens in Hong Kong in 1997 eventually killed six people, but the epidemic was stopped by the quick slaughter of millions of chickens in the area. This virus identified was classified as an avian flu (bird flu), H5N1 strain of influenza. As of August 2010, H5N1 influenza had claimed approximately 300 human lives, and the lethal virus had spread geographically to Europe and Africa. Up to that point, only a few cases of human-to-human transmission of H5N1 had been documented. However, because of its lethality, the H5N1 virus was closely monitored by epidemiologists for signs that the virus could mutate in such a way that it could transmit easily between humans, a necessary step toward pandemic level outbreaks.

Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, works at his desk.

Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, works at his desk. As scientists mark the 100th anniversary of the Spanish influenza pandemic, labs around the country are hunting better vaccines to “We have to do better and by better, we mean a universal flu vaccine. A vaccine that is going to protect you against essentially all, or most, strains of flu,” said Fauci.
(AP Photo/Carolyn Kaster)


Antiviral drugs are used to treat influenza. They are prescription drugs that fight the flu virus found within the human body. Antiviral drugs affect viral infections, which are different from antibiotics, which fight bacterial infections. Both drugs, however, lessen the associated symptoms and shorten the time that one is sick. Antiviral drugs also prevent serious flu complications, like pneumonia. In addition, for persons who are exceptionally susceptible for having serious complications from the flu, antiviral drugs minimize these people's risk from a more serious illness or even death.

Public health role and response

A single-celled microorganism, which does not possess any distinct nuclei or complex cell structures, that is responsible for many diseases.
A chemical secreted by an endocrine gland and some nerve cells, which regulates the function of a specific organ or tissue.
A medical substance that is administered to stimulate the immune system to produce antibodies, which results in disease-causing microbes to become weakened or die.
A submicroscopic parasitic particle of a nucleic acid, which is surrounded by a protein, that can only replicate itself within a host cell.

More detailed information is provided on the flu.gov website under Pandemic Flu ( http://www.flu.gov/planning-preparedness/federal/index.html ).


People can minimize their risk for getting influenza during a pandemic by following several simple guidelines. When these guidelines are followed the prognosis for surviving such an pandemic is good. These guidelines are:



Enacting controls on pig and poultry farms may be an important way to prevent the rise of a new influenza pandemic. Some influenza researchers recommend that pigs and domestic ducks and chickens not be raised together. Separating pigs and fowl at live markets may also be a sensible precaution. With the concentration of poultry and pigs at factory farms, it is important for farmers, veterinarians, and public health officials to monitor these farms for influenza. Any action to control flu must be an international effort, because the influenza virus moves rapidly without respect to national borders.

While not completely able to prevent influenza, flu vaccines are able to minimize one's chances of getting the flu. Medical professionals consider flu vaccines as the better way to prevent influenza when compared with antiviral drugs, which are normally used to fight the illness once it occurs.

See also Avian flu ; Centers for Disease Control and Prevention ; H1N1 influenza A (2009) ; Pandemic ; U.S. Department of Health and Human Services ; World Health Organization .



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American Medical Association, 515 N. State St., Chicago, IL, 60654, (800) 621-8335, http://www.ama-assn.org/ .

Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA, 30333, (800) 232-4636, cdcinfo@cdc.gov, http://www.cdc.gov/ .

World Health Organization, Avenue Appia 20, Geneva, Switzerland, 1211 27, 41 22 791-2111, Fax: 41 22 7913111, cdcinfo@cdc.gov, http://www.who.int/en/ .

Angela Woodward
Revised by William A. Atkins, BB, BS, MBA

  This information is not a tool for self-diagnosis or a substitute for professional care.