The Hong Kong flu, also known as the 1968 flu pandemic, was an influenza pandemic that occurred between 1968 and 1970 and which killed between one and four million people globally. 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.
History
Origin and outbreak in Hong Kong and China
The first recorded instance of the outbreak appeared on 13th July 1968 in British Hong Kong. It has been speculated that the outbreak began in mainland China before it spread to Hong Kong: On 11th July, before the outbreak in the colony was first noted, the Hong Kong newspaper Ming Pao reported an outbreak of respiratory illness in Guangdong Province, and the next day, The Times issued a similar report of an epidemic in southeastern China. Later reporting suggested that the flu had spread from the central provinces of Sichuan, Gansu, Shaanxi, and Shanxi, which had experienced epidemics in the spring. However, due to a lack of etiological information on the outbreak and a strained relationship between Chinese health authorities and those in other countries at the time, it cannot be ascertained whether the Hong Kong virus was to blame.
The outbreak in Hong Kong reached its maximum intensity in two weeks. 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.
There were two waves of the flu in mainland China, one between July and September in 1968 and the other between June and December in 1970. The reported data were very limited due to the Cultural Revolution, but retrospective analysis of flu activity between 1968 and 1992 shows that flu infection was the most serious in 1968, implying that most areas in China were affected at the time.
International spread
Despite the lethality of the 1957–1958 pandemic in China, little improvement had been made regarding the handling of such epidemics.
By 13 August, it was clear to virologists that strains isolated from the outbreak in Hong Kong differed markedly from previous strains of influenza. However, they were not at the time considered to be an entirely new subtype of influenza A, only a variant of older strains. Nevertheless, the World Health Organization warned of potential worldwide spread of the virus on 16 August. An outbreak of influenza-like illness in Singapore during the second week of August was the first indication of spread outside of Hong Kong. Around the same time, an outbreak became apparent in the Philippines and Malaysia, and, before the end of the month, an epidemic was underway in the Republic of Vietnam.
In September 1968, the flu reached India, northern Australia, Thailand, and Europe. The same month, the virus entered the United States and was carried by troops returning from the Vietnam War, but it did not become widespread in the country until December 1968.
In the USSR, the first cases of the flu began to appear in mid-December.
It reached South America by 1969.
The development of the pandemic at first resembled that of the 1957 pandemic, which had spread unencumbered throughout the spring and summer and had become truly worldwide by October, by which point nearly all countries were experiencing their first or even second wave. However, the two experiences eventually diverged within a couple of months after their initial outbreaks. In 1968, many countries (e.g., the United Kingdom, Japan) did not immediately see outbreaks despite repeated introductions of the virus throughout August and September. Additionally, after September, there was little evidence of continued spread in new areas, despite similar importations of the virus into those areas. Epidemics did eventually develop during the winter months, but these were often mild (especially when compared to the experience in the United States). In some countries (such as the UK and Japan), it was not until the following winter of 1969–1970 that truly severe epidemics developed.
At the time of the outbreak, the Hong Kong flu was also known as the "Mao flu" or "Mao Tse-tung flu". The name "Hong Kong flu" was not used within the colony, where the press dubbed it the "killer flu" after the first several deaths. Before the end of July, the South China Morning Post predicted that "Fingers of scorn" would be directed at Hong Kong in the coming weeks and stated that the colony had "acted, unwillingly, in our old role as an entrepot for a sneeze". (An outbreak of influenza in Hong Kong had been the first one to occur outside of mainland China during the 1957–1958 pandemic and had been what alerted the rest of the world to the developing situation, when international press began to report on it.)
Denny Huang, a member of the Urban Council of Hong Kong, later decried the widespread adoption of the name "Hong Kong flu", claiming that it was "giving Hong Kong a bad name". He asked why foreign press and health authorities did not refer to it by its "proper name—China flu". China certainly did not escape associations with the new virus, however, as the name "Mao flu" suggests. It was speculated even at the time that the virus had originated from "Red China". These differing names for the flu resulted in some confusion: In January 1969, a British member of parliament asked David Ennals, the Secretary of State for Social Services, "in what way the characteristics of Mao flu can be distinguished from those of Hong Kong flu". In addition to these names, the virus was also often referred to as "Asian flu" or "Asiatic flu", as it was not yet considered an entirely different subtype from the previously circulating influenza A.
Worldwide deaths from the virus peaked in December 1968 and January 1969, when public health warnings and virus descriptions had been widely issued in the scientific and medical journals. Isolated countries like Albania reported the first cases of the flu in December 1969, reaching a peak in infections in the first months of the year 1970. 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.
Asia
On 8 September 1968, the ship S.S. Rajula docked at Madras (present-day Chennai) from Singapore, where influenza had been epidemic the month before. On board were 16 people who were suspected to have influenza infections, a number of which were confirmed to be caused by the pandemic virus. On 9 September, only eight cases of typical influenza were reported in city hospitals, but by 17 September the number had reached 7,661, after which incidence of the disease declined to just 68 cases on 31 October.
The epidemic thereafter spread throughout Madras State. Pandemic influenza was reported in Chengalpattu, Kanchipuram, Pondicherry, Vellore, Coimbatore, and the Nilgiris district during the second half of September; in Madurai, Tiruppur, Karur, Tiruchirappalli, Thanjavur, and Palani during the first half of October; and in Tirunelveli, Ramanathapuram, and Salem during the middle and second half of October. The epidemic then declined in the latter part of November and December.
Although the epidemic in Madras State seemed to originate from Madras upon the arrival of S.S. Rajula, two strains of the pandemic virus were in fact isolated at the end of August elsewhere, namely Coonoor and Ooty, suggesting that the virus had likely already been seeded prior to its apparent importation from Singapore on 8 September.
Concurrent with the outbreak in Madras State was a moderate epidemic in Bombay (present-day Mumbai), which began the second week of September and subsided in October.
There was a recurrence of influenza in December 1969, when a "considerable increase" in the disease was reported in several states.
During the second week of September, nearly 2000 participants from 92 countries, including some in southeast Asia where the flu was epidemic, met in Tehran for the Eighth International Congresses on Tropical Medicine and Malaria. An outbreak of influenza soon erupted among the participants, afflicting at least a third of them. The convention was the apparent origin of a broader outbreak within the capital city, which thereafter spread rapidly throughout Iran.
The virus entered Japan repeatedly throughout August and September via importations from Hong Kong and other countries already afflicted, but these introductions did not spark any larger outbreak. The first "true epidemic" began in early October, confined almost entirely to school settings. It was not until January 1969 that the outbreak began to develop the typical features of an epidemic among the general population, although it remained moderate in its extent and spread less rapidly than expected for an outbreak of a novel influenza virus. The epidemic was reported to be still increasing on 6 February, spreading from the larger cities into the smaller cities, towns, and villages, though the rural areas were relatively less affected. By 13 March, the epidemic had mostly subsided within the large cities.
During this same period, an epidemic of influenza B affected the whole country, including rural parts. For this reason, it is difficult to ascertain the extent to which the pandemic virus and the seasonal B virus each contributed to the general wave of influenza-like illness that occurred between January and February 1969.
A second pandemic wave developed in Japan towards the end of November 1969 and subsided in January 1970. This outbreak was more localized within the east of the middle part of the country, around Tokyo. Like that in many countries of Europe, the second wave in Japan was more severe than the first. While the 1968–1969 wave saw excess pneumonia and influenza and all-cause mortality rates of 5.4 and 27.0 per 100,000, respectively, the 1969–1970 wave saw rates of 11.3 and 49.1 per 100,000, respectively. In sum, approximately two thirds of the total pandemic mortality occurred over the winter of 1969–1970.
Oceania
The pandemic reached Australia in September 1968, resulting in a severe epidemic among the general population of the Northern Territory; however, no further outbreaks were reported elsewhere until the following year. Generally mild outbreaks began to be reported in mid-May 1969. In Melbourne, influenza broke out in the suburbs in mid-June, developing into an epidemic that peaked about 20 July and had subsided by mid-August. In Sydney, the disease broke out at the beginning of July and continued into August. Another epidemic, more widespread and severe than the first, afflicted the Northern Territory in 1969.
Australia experienced another pandemic wave in 1970, reportedly more widespread than that of 1969. Queensland saw a widespread epidemic of high incidence between 1 June and early July. Between 10 June and mid-August, a widespread epidemic, also of high incidence, affected New South Wales, particularly Sydney. A moderate outbreak driven by the pandemic virus alongside other respiratory viruses affected Victoria between mid-June and August, followed by a secondary outbreak, involving some influenza B, that subsided in mid-September. For the third year in a row, the Northern Territory experienced an epidemic of the pandemic virus, though the disease was less severe than in 1968 and 1969.
Similar to Japan and countries in Europe, Australia in general experienced a more severe second wave of the pandemic as compared with the first. While the first wave of 1969 produced excess pneumonia and influenza and all-cause mortality rates of 4.0 and 23.5 per 100,000, respectively, the second wave resulted in excess mortality rates of 14.1 and 63.8 per 100,000, respectively.