Hong Kong Flu

Influenza (Flu)
Types Avian A/H5N1 subtype Canine Equine Swine A/H1N1 subtype
Vaccines 2009 pandemic Pandemrix Live attenuated Seasonal flu vaccine brands
Treatment Amantadine Laninamivir Oseltamivir Peramivir Rimantadine Umifenovir Vitamin D Zanamivir
Pandemics 1918 Spanish flu 1957 Asian flu 1968–1969 Hong Kong flu 2009 swine flu
Outbreaks 1976 swine flu 2006 H5N1 India 2007 Australian equine 2007 Bernard Matthews H5N1 2008 West Bengal 2015 United States H5N2 outbreak
See also Flu season Influenza evolution Influenza research Influenza-like illness Vaccine reformulations
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The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic whose outbreak in 1968 and 1969 killed between one and four million people globally.^{[1][2][3][4][5]} It is among the deadliest pandemics in history, and was caused by an H3N2 strain of the influenza A virus. The virus was descended from H2N2 (which caused the Asian flu pandemic in 1957–1958) through antigenic shift—a genetic process in which genes from multiple subtypes are reassorted to form a new virus.^[6][7][8]

History[edit | edit source]

Origin and outbreak in Hong Kong and China[edit | edit source]

The first recorded instance of the outbreak appeared on 13 July 1968 in British Hong Kong.^{[8][10][11][12]} There is an unconfirmed possibility that the outbreak actually began in Mainland China before it spread to Hong Kong.^[11][13]

The outbreak in Hong Kong, where the population density was greater than 6,000 people per square kilometre (20,000 per sq. mi.), reached its maximum intensity in two weeks.^[11][12] The outbreak lasted around six weeks, affecting about 15% of the population (some 500,000 people infected), but the mortality rate was low and the clinical symptoms were mild.^{[11][12][14][15]}

There were two waves of the flu in mainland China, one between July–September in 1968 and the other between June–December in 1970.^[15] The reported data were very limited due to the Cultural Revolution, but retrospective analysis of flu activity between 1968–1992 shows that flu infection was the most serious in 1968, implying that most areas in China were affected at the time.^[15]

Outbreaks in other areas[edit | edit source]

By the end of July 1968, extensive outbreaks were reported in Vietnam and Singapore.^[12] Despite the lethality of the 1957 Asian Flu in China, little improvement had been made regarding the handling of such epidemics.^[12] The Times was the first source to report the new possible pandemic.^[12]

By September 1968, the flu had reached India, the Philippines, northern Australia, and Europe. The same month, the virus entered California and was carried by troops returning from the Vietnam War, but it did not become widespread in the United States until December 1968. It reached Japan, Africa, and South America by 1969.^[16] At the time of the outbreak, the Hong Kong flu was also known as the "Mao flu" or "Mao Tse-tung flu".^{[17][18][19][20]}

Worldwide deaths from the virus peaked in December 1968 and January 1969, when public health warnings^[21] and virus descriptions^[22] had been widely issued in the scientific and medical journals. In Berlin, the excessive number of deaths led to corpses being stored in subway tunnels, and in West Germany, garbage collectors had to bury the dead because of a lack of undertakers. In total, East and West Germany registered 60,000 estimated deaths. In some areas of France, half of the workforce was bedridden, and manufacturing suffered large disruptions because of absenteeism. The UK postal and rail services were also severely disrupted.^[23]

Vaccine and aftermath[edit | edit source]

Four months into the Hong Kong flu pandemic, American microbiologist Maurice Hilleman and his team had created a vaccine and more than 9 million doses had been manufactured.^[24][25] The same team also played a key role in developing a vaccine during the 1957–58 Asian flu pandemic.^[25][26]

The H3N2 virus returned during the following 1969–70 flu season, which resulted in a second, deadlier wave of deaths in Europe, Japan, and Australia.^[27] It remains in circulation today as a strain of seasonal flu.^[2]

Clinical data[edit | edit source]

Flu symptoms typically lasted four to five days, but some cases persisted for up to two weeks.^[16]

Virology[edit | edit source]

The Hong Kong flu was the first known outbreak of the H3N2 strain, but there is serologic evidence of H3N1 infections in the late 19th century. The virus was isolated in Queen Mary Hospital.^[28]

The H2N2 and H3N2 pandemic flu strains both 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 (such as many poultry species), and direct transmission of avian viruses to humans is possible. H1N1, associated with the 1918 flu pandemic, may have been transmitted directly from birds to humans.^[29]

The Hong Kong flu strain shared internal genes and the neuraminidase with the 1957 Asian flu (H2N2). Accumulated antibodies to the neuraminidase or internal proteins may have resulted in many fewer casualties than most other pandemics. However, cross-immunity within and between subtypes of influenza is poorly understood.^{[citation needed]}

The basic reproduction number of the flu in this period was estimated at 1.80.^[30]

• 

  This negatively-stained transmission electron microscopic (TEM) image revealed the presence of a number of Hong Kong Flu virus virions, the H3N2 subtype of the Influenza A virus. Note the proteinaceous coat, or capsid, surrounding each virion, and the hemagglutinin-neuraminidase spikes, which differ in terms of their molecular make-up from strain to strain.

• 

  The influenza viruses that caused the Hong Kong flu (magnified approximately 100,000 times)

Mortality[edit | edit source]

The estimates of the total death toll due to Hong Kong flu (from its beginning in July 1968 until the outbreak faded during the winter of 1969–70^[31]) vary:

• The World Health Organization and Encyclopaedia Britannica estimated the number of deaths due to Hong Kong flu to be between 1 and 4 million globally.^[1][17]
• The United States Centers for Disease Control and Prevention (CDC) estimated that, in total, the virus caused the deaths of 1 million people worldwide.^[32]

However, the death rate from the Hong Kong flu was lower than most other 20th-century pandemics.^[16] The World Health Organization estimated the case fatality rate of Hong Kong flu to be lower than 0.2%.^[1] The disease was allowed to spread through the population without restrictions on economic activity, and a vaccine created by American microbiologist Maurice Hilleman and his team became available four months after it had started.^[23][24][25] Fewer people died during this pandemic than in previous pandemics for several reasons:^[32]

1. Some immunity against the N2 flu virus may have been retained in populations struck by the Asian Flu strains that had been circulating since 1957.
2. The pandemic did not gain momentum until near the winter school holidays in the Northern Hemisphere, thus limiting the infection's spread.
3. Improved medical care gave vital support to the very ill.
4. The availability of antibiotics that were more effective against secondary bacterial infections.

By region[edit | edit source]

For this pandemic, there were two geographically-distinct mortality patterns. In North America (the United States and Canada), the first pandemic season (1968/69) was more severe than the second (1969/70). In the "smoldering" pattern seen in Europe and Asia (United Kingdom, France, Japan, and Australia), the second pandemic season was two to five times more severe than the first.^[27] The United States health authorities estimated that about 34,000^[33][34] to 100,000^[32] people died in the U.S; most excess deaths were in those aged 65 and older.^[35]

See also[edit | edit source]

• Influenza vaccine

References[edit | edit source]

External links[edit | edit source]

• Influenza Research Database – Database of influenza genomic sequences and related information.