Hong Kong flu
Encyclopedia
- See Flu for details about the illnesses and H3N2H3N2Influenza A virus subtype H3N2 is a subtype of viruses that cause influenza . H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains...
for details about the causative agent.
The Hong Kong flu was a category 2
Pandemic Severity Index
The Pandemic Severity Index is a proposed classification scale for reporting the severity of influenza pandemics in the United States. The PSI was accompanied by a set of guidelines intended to help communicate appropriate actions for communities to follow in potential pandemic situations...
flu pandemic whose outbreak in 1968 and 1969 killed an estimated one million people worldwide. It was caused by an H3N2
H3N2
Influenza A virus subtype H3N2 is a subtype of viruses that cause influenza . H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains...
strain of the influenza A virus, descended from H2N2
H2N2
H2N2 is a subtype of the type influenzavirus A. H2N2 has mutated into various strains including the Asian flu strain , H3N2, and various strains found in birds...
through antigenic shift
Antigenic shift
Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains...
, a genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
process in which gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s from multiple subtypes reassorted
Reassortment
Reassortment is the mixing of the genetic material of a species into new combinations in different individuals. Several different processes contribute to reassortment, including assortment of chromosomes, and chromosomal crossover. It is particularly used when two similar viruses that are infecting...
to form a new virus.
The 1968-1969 pandemic
The first record of the outbreak in Hong KongHong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
appeared on 13 July 1968. By the end of July 1968, extensive outbreaks were reported in Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
and Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
. Despite the fatality of the 1957 Asian Flu
Asian flu
Asian Flu may refer to:* The Asian Financial Crisis of 1997, or* Asian Flu, the H2N2 virus...
in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, little improvement had been made regarding the handling of such epidemic
Epidemic
In epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...
s. The Times
The Times
The Times is a British daily national newspaper, first published in London in 1785 under the title The Daily Universal Register . The Times and its sister paper The Sunday Times are published by Times Newspapers Limited, a subsidiary since 1981 of News International...
newspaper was actually the first source to sound alarm regarding this new possible pandemic
Pandemic
A pandemic is an epidemic of infectious disease that is spreading through human populations across a large region; for instance multiple continents, or even worldwide. A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic...
.
By September 1968, the flu reached India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. That same month, the virus entered California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
from returning Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...
troops but did not become widespread in the US until December 1968. It would reach Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Africa and South America by 1969.. The outbreak in Hong Kong, where density is about 500 people per acre, reached maximum intensity in 2 weeks, lasting 6 weeks in total from July to December 1968, however worldwide deaths from this virus peaked much later, in December 1968 and January 1969. By that time, public health warnings and virus descriptions were issued in the scientific and medical journals.
In comparison to other pandemics, the Hong Kong flu yielded a low death rate, with a case-fatality ratio below 0.5% making it a category 2 disease on the Pandemic Severity Index
Pandemic Severity Index
The Pandemic Severity Index is a proposed classification scale for reporting the severity of influenza pandemics in the United States. The PSI was accompanied by a set of guidelines intended to help communicate appropriate actions for communities to follow in potential pandemic situations...
. The pandemic infected an estimated 500,000 Hong Kong residents, 15% of the population. In the United States, approximately 33,800 people died.
The same virus returned the following years: a year later, in late 1969 and early 1970, and in 1972.
Fewer people died during this pandemic than the two previous pandemics for various reasons:
- some immunity against the N2 flu virus may have been retained in populations struck by the Asian FluAsian fluAsian Flu may refer to:* The Asian Financial Crisis of 1997, or* Asian Flu, the H2N2 virus...
strains which had been circulating since 1957; - the pandemic did not gain momentum until near the winter school holidays, thus limiting the infection spreading;
- improved medical care gave vital support to the very ill;
- the availability of antibiotics that were more effective against secondary bacterial infections.
Clinical data
Flu symptoms lasted 4 to 5 days.Those over the age of 65 were most likely to die.
Virology
H3N2
Influenza A virus subtype H3N2 is a subtype of viruses that cause influenza . H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains...
strain, though there is serologic evidence of H3N1 infections in the late 19th century.
The virus was isolated in Queen Mary Hospital
Queen Mary Hospital, Hong Kong
Queen Mary Hospital , located in Pok Fu Lam on Hong Kong Island of Hong Kong, is the flagship teaching hospital of the Faculty of Dentistry and Li Ka Shing Faculty of Medicine of the University of Hong Kong...
.
In the 1968 pandemic vaccine became available one month after the outbreaks peaked in the US.
Both the H2N2
H2N2
H2N2 is a subtype of the type influenzavirus A. H2N2 has mutated into various strains including the Asian flu strain , H3N2, and various strains found in birds...
and H3N2 pandemic flu strains contained genes from avian influenza viruses. The new subtypes arose in pigs coinfected with avian and human viruses and were soon transferred to humans. Swine were considered the original "intermediate host" for influenza, because they supported reassortment of divergent subtypes. However, other hosts appear capable of similar coinfection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible. H1N1 may have been transmitted directly from birds to humans (Belshe 2005).
The Hong Kong flu strain shared internal genes and the neuraminidase
Neuraminidase
Neuraminidase enzymes are glycoside hydrolase enzymes that cleave the glycosidic linkages of neuraminic acids. Neuraminidase enzymes are a large family, found in a range of organisms. The most commonly known neuraminidase is the viral neuraminidase, a drug target for the prevention of the spread...
with the 1957 Asian Flu
Asian flu
Asian Flu may refer to:* The Asian Financial Crisis of 1997, or* Asian Flu, the H2N2 virus...
(H2N2
H2N2
H2N2 is a subtype of the type influenzavirus A. H2N2 has mutated into various strains including the Asian flu strain , H3N2, and various strains found in birds...
). Accumulated antibodies to the neuraminidase or internal proteins may have resulted in much fewer casualties than most pandemic
Pandemic
A pandemic is an epidemic of infectious disease that is spreading through human populations across a large region; for instance multiple continents, or even worldwide. A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic...
s. However, cross-immunity within and between subtypes of influenza is poorly understood.
"Three strains of Hong Kong influenza virus isolated from humans were compared with a strain isolated from a calf for their ability to cause disease in calves. One of the human strains. A/Aichi/2/68, was detected for five days in a calf, but all three failed to cause signs of disease. Strain A/cal/Duschanbe/55/71 could be detected for seven days and caused an influenza-like illness in calves."
External links
- Influenza Research Database – Database of influenza genomic sequences and related information.