During the 20th century, two influenza pandemics began in Asia and spread around the world.
The Asian Flu Pandemic of 1957-58 began in southern China, infecting 1-4 million people world-wide. A decade later, the Hong Kong Flu infected an estimated 1-3 million people around the globe.
Deadly genetic mixtures of human flu with bird or swine variants, these viruses targeted vulnerable young or elderly victims.
Since the mid-20th century, medical professionals have watched with alarm as different strains of swine or avian flu jump into the human population. Thus far, however, Asia has not produced another global pandemic.
The Asian Flu of 1957-58 (subtype H2N2):
In February, 1957, a new strain of influenza was found in East Asia. Originating in Guizhou, a province in south-central China, the virus quickly spread to Singapore. Hong Kong reported cases in April, and the disease hit the US in June.
The Asian Flu was identified as a form of avian influenza, normally found in wild ducks, which had crossed with a human virus. It was named H2N2; the H and N numbers designate the proteins on the outside of the virus that bind to target cells in the victim.
Since influenza is a sloppy sort of virus, it easily recombines and mutates - and human immune systems cannot always keep pace.
The Human Toll of the Asian Flu Pandemic:
The 1957-58 pandemic was rated a category 2 out of 7 on the Pandemic Severity Index, with a 7 being "apocalyptic." [The so-called Spanish Flu Pandemic of 1918, which killed as many as 100 million people world-wide, rates a 5.]
According to the Johns Hopkins School of Public Health, the Asian Flu killed almost 2 million people around the globe, including some 69,800 in the United States. It was most deadly for the elderly.
The flu seemed to have burned itself out by December of 1957, but in January and February of 1958, a "second wave" struck. This rebound effect is not uncommon during influenza epidemics, as the virus finds a new pool of people to infect. It also remained in the wild duck population.
The Hong Kong Flu of 1968-69 (subtype H3N2):
People who survived the 1957-58 Asian Flu pandemic had developed resistance to the H2N2 virus responsible for the outbreak. However, during the next decade the virus mutated by changing its H antigen - the hemagglutinin - and enough people's immune systems were fooled by the change to spark a pandemic of the new H3N2 subtype. The virus likely combined and incubated in pigs, who then transferred it to human carriers.
As the common name indicate, the H3N2 flu strain was first detected in Hong Kong in July of 1968; the illness spread explosively in Hong Kong's tightly-packed population, but the death rate was very low.
Hong Kong Flu Goes International:
Perhaps because only a single antigen had changed between the 1957 outbreak and the 1968 one, the virus spread quickly but was not as severe as that responsible for the Asian Flu Pandemic.
Within a month of its discovery in Hong Kong, it had spread to Vietnam and Singapore. By September, the virus had reached the Philippines, India, northern Australia, the U.K., continental Europe, and the United States. Troop movements during the Vietnam War helped the disease to spread internationally.
In January of 1969, Japan reported its first cases of H3N2, while South Africa and South America were spared until mid-1969.
The Human Toll of the Hong Kong Flu Pandemic:
World-wide, an estimated 500,000 people died in the Hong Kong Flu pandemic. Again, the elderly were the hardest hit.
In the United States, approximately 33,800 people were killed by the H3N2 strain.
Asian Influenza Pandemic Scares in the Late 20th Century:
Since 1969, epidemiologists and the media alike have focused a lot of attention on Asia as the possible source of further influenza pandemics.
In 1977, children in northern China fell victim to what was named the "Russian Flu," H1N1. It spread around the world, but mostly infected people under the age of 23 - those who had not been born at the time of the Hong Kong Flu pandemic.
In 1997 and 1999, new versions of avian influenza crossed into humans in China and Southeast Asia, sparking fear of new pandemics. However, these strains did not pass easily from human to human, and the outbreaks were contained.
Prospects for the Future:
Much of East and Southeast Asia is densely populated with people, chickens, ducks, pigs, and other livestock. Wild birds and animals, also possible reservoirs for influenza, move around cities and rural areas as well.
In this environment, the influenza virus has ample opportunity to mix and mingle with other strains.
However, medical science has advanced remarkably since 1969. Speedy diagnosis of new strains of influenza offer hope of quick treatment for victims. Electric ventilators and anti-viral medications also will cut the death toll in any future pandemic.
Influenza is a sly and sometimes deadly opponent, but with each passing year, humanity is better learning how to combat it.
Youri Ghendon, "Introduction to Pandemic Influenza through History," European Journal of Epidemiology Vol. 10 No. 4 (Aug. 1994), pp. 451-3.
Arthur E. Starling, Plague, SARS and the Story of Medicine in Hong Kong. (Hong Kong: Hong Kong University Press, 2006).
Richard J. Webby and Robert G. Webster, "Are We Ready for Pandemic Influenza?" Science Vol. 302 No. 5650 (Nov. 28, 2003), pp. 1519-22.
"Pandemics and Pandemic Scares in the 20th Century," National Vaccine Program Office, US Department of Health & Human Services (updated Feb. 12, 2004).
"Homeland Security: Pandemic Influenza," GlobalSecurity.org (accessed April 26, 2009).
"Historic Television Program Offers Unique Perspective of 1957 Asian Flu Pandemic," Johns Hopkins, Bloomberg School of Public Health (Feb. 22, 2006).