Pandemic

Map of the world showing the countries that affected the pandemic influenza A(H1N1) in 2009.

Total confirmed cases of COVID-19 by millions of people as at 20 June 2022.

A pandemic (from the Greek πανδημία, from παν, pan, "everything", and δήμος, demos, 'people', meaning 'all the people') is an epidemic of an infectious disease that has spread over a large geographical area, for example, across several continents or around the world, affecting a considerable number of people.

Throughout human history, there have been a number of pandemics of diseases such as smallpox. The most fatal pandemic in recorded history was the Black Death (also known as The Plague), which killed an estimated 75 to 200 million people in the 14th century. The term was not yet used, until later pandemics, including the 1918 flu pandemic.

Current pandemics include tuberculosis, COVID-19 (SARS-CoV-2), and HIV/AIDS.

Definition

It is a disease that spreads to many countries and continents, crosses a large number of borders, exceeds the number of expected cases and persists over time; in addition, it attacks almost all the individuals of a locality or region. A pandemic is an epidemic that occurs on a scale that crosses international borders and generally affects people worldwide. A disease or condition, because it is widespread or causes many deaths, is not a pandemic, as it must have an infectious character. For example, cancer is responsible for many deaths, but it is not considered a pandemic because the disease is not contagious (meaning, easily transmissible) and it is not infectious either.

Evaluation

Stages

The World Health Organization (WHO) previously applied a six-stage classification to describe the process by which a new virus progresses from the first human infections to being considered a pandemic. It starts when most animals are infected with a virus and some cases where animals infect people, then moves to the stage where the virus begins to be transmitted directly between people, and ends with the stage where human infections with the virus have spread throughout the world. In February 2020, a WHO spokesperson clarified that "there is no official category for a pandemic".

World Health Organization (WHO) pandemic phase descriptions of influenza

At a virtual press conference in May 2009 on the influenza pandemic, Dr Keiji Fukuda, WHO's acting Assistant Director-General for Health Security and Environment said: "An easy way to think of a pandemic... is: a pandemic is a global outbreak. So you might ask: "What is a global outbreak?" Global outbreak means we see both the spread of the agent...and then we see disease activities in addition to the spread of the virus".

In planning for a potential influenza pandemic, WHO published a document on pandemic preparedness guidance in 1999, revised in 2005 and 2009, defining the phases and appropriate actions for each phase in an aide-mémoire titled Descriptions of the phases of the WHO pandemic and main actions by phase. The 2009 revision, including descriptions of a pandemic and the phases leading to its declaration, was finalized in February 2009. The 2009 H1N1 pandemic was not on the horizon at the time nor was it mentioned in the document. All versions of this document refer to the flu. The phases are defined by the spread of the disease. Virulence and mortality are not mentioned in the current WHO definition, although these factors have been included previously.

Influenza Intervals in the CDC Pandemic Interval Framework

In 2014, the US Centers for Disease Control and Prevention introduced a framework analogous to the WHO pandemic stages called the Pandemic Interval Framework. It includes two pre-pandemic intervals,

• Research
• Recognition

and four pandemic intervals,

• Initiation
• Acceleration
• Deceleration
• Preparation

It also includes a table that defines the intervals and relates them to the WHO pandemic stages.^{[citation needed]}

Gravity

Hypothetical flu deaths estimates in the USA. U.S. From 2010 through variable values of lethality rate and accumulated incidence of infection. The selected estimated numbers of deaths are indicated with a black line, in each relevant combination of the accumulated lethality and incidence rate. The lethality rate is an example of a measure of clinical severity, and the cumulative incidence of infection is an example of a transmissibility measure in the Pandemic Gravity Assessment Framework.

Scaling examples of past flu pandemics and past seasons. A color scheme is included to represent the corresponding hypothetical estimates of flu deaths in the U.S. population. U.S. From 2010, with the same color scale as the previous figure.

In 2014, the United States Centers for Disease Control and Prevention adopted the Pandemic Severity Assessment Framework (PSAF) to assess the severity of pandemics. The PSAF replaced the linear index of severity of the 2007 pandemic, which assumed a 30% spread and a measured case fatality rate (TL or CFR) to assess the severity and evolution of the pandemic.

Historically, measures of pandemic severity were based on the case fatality rate. However, the case fatality rate might not be an adequate measure of pandemic severity during a pandemic response because:

• Deaths may be delayed for several weeks with respect to cases, which makes the lethality rate underestimated.
• The total number of cases may not be known, making the lethality rate an overestimation.
• A single rate of lethality for the entire population can conceal the effect on vulnerable subpopulations, such as children, the elderly, people with chronic diseases and members of certain racial and ethnic minorities.
• Deaths alone may not explain all the effects of the pandemic, such as absenteeism or demand for health services.

To account for the limitations of measuring the case fatality rate alone, the PSAF classifies the severity of a disease outbreak along two dimensions: clinical disease severity in infected persons; and the transmissibility of infection in the population. Each dimension can be measured using more than one metric, which are scaled to allow comparison of the different metrics. Instead, clinical severity can be measured, for example, as the ratio of deaths to hospitalizations or using genetic markers of virulence. Transmissibility can be measured, for example, as the basic reproductive rate R₀ and serial interval or by underlying population immunity. The framework provides guidelines for scaling the various measures and examples of assessing past pandemics using the framework.^{[citation needed]}

Historical Pandemics

There have been a significant number of pandemics in human history, all of them generally zoonoses, which have come with the domestication of animals, such as smallpox, diphtheria, influenza and tuberculosis. There have been a number of particularly important epidemics that deserve mention above the "mere" destruction of cities:

• The plague of Athens: During the Peloponnese War, 430 B.C., an unknown agent, possibly typhoid fever killed a quarter of the Athenian troops and a quarter of the population over four years. This fatally weakened the preeminence of Athens, but the absolute virulence of the disease prevented further expansion.

• The antonin pest, 165-180. Possibly smallpox brought from the Near East, killed a quarter of the infected and up to five million in total. At the most active moment of a second outbreak (251-266), it was said that 5000 people died a day in Rome.
• Justinian's plague began in 541. It was the first recorded outbreak of the bubonic plague. It began in the province of Egypt and reached Constantinople in the next spring. According to the Byzantine chronicler Procopio de Cesarea, the plague, at its most active time, killed 10 000 people per day, reducing the population of Constantinople by almost 40%. It continued to destroy even one quarter of the inhabitants of the Eastern Mediterranean.
• Black plague began in the centuryXIV. Eight hundred years after the last outbreak, the bubonic plague returned to Europe. Beginning in Asia, the disease reached the Mediterranean and Western Europe in 1348 (possibly carried by Italian merchants fleeing the war in Crimea), killing twenty million Europeans in six years, a quarter of the total population and up to half in the most affected urban areas.
• The typhus is the epidemic disease of wartime, and has been sometimes called "the fever of the camps" because of its pattern of erupting in times of hardship. Emergendo durante las Cruzadas, tuvo su primera impacto en Europa en 1489, en España. During the struggle between the Christian and Muslim Spaniards in Granada, Christians lost 3000 troops for war casualties and 20,000 for typhus. In 1528 the French lost 18,000 troops in Italy and lost the supremacy in Italy for the Spanish. In 1542, 30,000 people died of typhus while fighting the Ottomans in the Balkans. The disease also played a major role in the destruction of the Great Armée of Napoleon in Russia in 1811.
• The many epidemics that occurred due to the spread of European scouts to the populations of the rest of the world were mainly caused by the viruses of the Viruela and the Measles and are considered local eventualities of extraordinary virulence.
  • The diseases of the old continent killed much of the native population (guanche) of the Canary Islands in the sixteenth century.
  • Half of the native population of La Española Island died in 1518 by the smallpox.
  • The smallpox hit Mexico in the 1520s, where 150,000 people died only in Tenochtitlan, including the emperor.
  • In Peru, in the 1530s, the high mortality rate of natives helped the Spanish conquerors.
  • Measles killed two million more Mexican natives in the 1600s.
  • In addition, from 1848 to 1849, it is estimated that approximately 40,000 Hawaiian natives died, up to a total of 150,000 due to measles, cough and flu.
• The cholera - See: Cholera pandemics in Spain and [[Cólera (century)XIX)]].
  • First pandemic (1816-1826). Previously restricted to the Indian subcontinent, it began in Bengal and expanded through India to 1820. It spread to China and the Caspian Sea before it decreased.
  • The second pandemic (1829-1851) reached Europe, London in 1832, New York in the same year, and the Pacific coast in North America by 1834.
  • The third pandemic (1852-1860) mainly affected Russia, with more than one million deaths.
  • The fourth pandemic (1863-1875) was mostly spread by Europe and Africa.
  • The fifth pandemic (1899-1923) had little impact on Europe, thanks to progress in public health, but Russia was severely affected again.
  • The sixth pandemic, called “El Tor”, by the strain, began in Indonesia in 1961 and reached Bangladés in 1963, India in 1964, and the USSR in 1966.
  • The Latin American pandemic (1991-1993), which caused about 800,000 affected and around 7500 dead.
• The Russian influenza of 1889-1890, which originated in St.Petersburg, soon expanded for the rest of Europe and then to America. It caused a very low mortality of 1 per cent, but due to the large number of people affected, it is believed that it caused the death of about 1 000 000 people worldwide.
• The flu of 1918 (1918-1919). It started in March 1918 in Fort Riley, Kansas, United States. A severe and deadly flu strain spread throughout the world. The disease killed 25 million people over the course of six months; some estimate the total number of deaths worldwide in more than twice that number. Of these, they are estimated at around 10-17 million deaths in British India, 600,000 in the United States, 400,000 in France and Italy, 250,000 in the United Kingdom and 200,000 in Spain, among others. It faded in 18 months, and the concrete strain was H1N1.
• La Asian flu 1957. It originated in China and killed more than 1 million people around the world.
• La Hong Kong flu 1968. It caused about 1 million deaths globally, of which about half were generated in Hong Kong, then British territory, in a period of two weeks.
• The Russian flu of 1977. It affected only the population under 25 years of age. The number of victims is around 700,000.
• HIV/AIDS (1981-). It is the disease that consists of the inability of the immune system to deal with infections and other pathological processes. It is considered pandemic due to its rapid spread. Surged in Central Africa, it expanded to the five continents. Their victims are estimated at between 20 and 25 million, particularly in Africa.
• Severe Acute Respiratory Syndrome (SARS) of 2002. It emerged in the province of Guangdong in China. It affected 8098 people, covering 774 fatalities, the vast majority in Southeast Asia.
• The 2003 avian flu, in its H5N1 strain, became a pandemic threat in 2005, when the first contagions occurred in humans. However, although millions of poultry had to be sacrificed, mainly in Southeast Asia, only a few dozen victims had to be lamented in the human population.
• Influenza A (H1N1), also known as swine flu (2009-2010), was an infectious disease caused by a variant of the Influenzavirus A (subtype H1N1). The World Health Organization (WHO) classified it as a pandemic for fourteen months, during which it expanded from its origin in Mexico to the rest of the world. It had low mortality relative to its wide distribution (11-21 % of the infected world population), leaving behind between 150,000 and 575,000 fatalities.
• Ebola. Since its inception in 1976, there have been several outbreaks of this disease, always in sub-Saharan Africa, and the most important was 2014-2016, which caused more than 11 000 deaths.
• The COVID-19 pandemic, produced by the SARS-CoV-2 coronavirus (2019-2021). The SARS-CoV-2 made its appearance in the city of Wuhan, capital of Hubei province, west of Shanghai. On 11 February 2020, the World Health Organization officially called it COVID-19, and one month later, on 11 March, it was declared the status of pandemic for the expansion of the virus. SARS-CoV-2 spreads very fast and has average mortality, leaving more than 6.73 million confirmed deaths (January 2023).

There are also several unknown diseases that were extremely serious but have now vanished, so that their etiology cannot be determined. For example, the aforementioned plague of Greece in 430 B.C. C. and the English sweat of England in the XVI century, which struck down people in an instant and that it was much more feared than the bubonic plague.^{[citation needed]}

Conditions for a possible viral pandemic

The WHO indicates that, for a pandemic to appear, it is necessary:

• That a new microorganism appears, that has not circulated previously and therefore there is no immune population to it.
• May the microorganism be able to produce serious cases of disease or death.
• That the microorganism has the ability to transmit from person to person effectively.

Classification proposed by the WHO for influenza pandemics:

Additional bibliography

• Daniel-Henri Pageaux, coord., Pandemic and Culture, Madrid, Instituto Juan Andrés de Comparatística y Globalización (Series Humanistic Methodologies), 2021.