The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic whose outbreak in 1968 and 1969 killed an estimated one to four million people globally. It was caused by an H3N2 strain of the influenza A virus, which is descended from H2N2 through antigenic shift, a genetic process in which genes from multiple subtypes are reassorted to form a new virus.
History
The first recorded instance of the outbreak appeared on 13 July 1968 in Hong Kong. There is an unconfirmed possibility that the outbreak actually began in Mainland China before it spread to Hong Kong. By the end of July 1968, extensive outbreaks were reported in Vietnam and Singapore. Despite the lethality of the 1957 Asian Flu in China, little improvement had been made regarding the handling of such epidemics. The Times was the first source to report the new possible pandemic. 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. 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 British postal and train services were also severely disrupted. The outbreak in Hong Kong, where the population density was greater than 6,000 people per square kilometre, reached its maximum intensity in two weeks. The outbreak lasted six months in total, from July to December 1968. 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. The death rate from the Hong Kong flu was lower than for other 20th-century pandemics. The disease was allowed to spread through the population without restrictions on economic activity until a vaccine became available four months after it had started. The H3N2 virus returned during the following 1969/70 flu season, which resulted in a second, deadlier wave of deaths. It remains in circulation today as a strain of seasonal flu.
Clinical data
Flu symptoms typically lasted four to five days, but some cases persisted for up to two weeks.
Virology
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. 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, 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. The Hong Kong flu strain shared internal genes and the neuraminidase with the 1957 Asian flu. 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. The basic reproduction number of the flu in this period was estimated at 1.80.
Mortality
The United States Centers for Disease Control and Prevention estimated that in total, the virus killed one million people worldwide from its beginning in July 1968 until the outbreak faded during the winter of 1969–70. The CDC estimated that about 34,000 to 100,000 people died in the U.S; most excess deaths were in those 65 and older. However, fewer people died during this pandemic than in previous pandemics for several reasons:
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.
The pandemic did not gain momentum until near the winter school holidays, thus limiting the infection's spread.
Improved medical care gave vital support to the very ill.
For this pandemic, there were two geographically-distinct mortality patterns. In North America, the first pandemic season was more severe than the second. In the "smoldering" pattern seen in Europe and Asia, the second pandemic season was two to five times more severe than the first.
