The 1968 influenza pandemic (the "Hong Kong flu") was a category 2 flu pandemic whose outbreak in 1968 and 1969 killed an estimated one million people worldwide. Hong Kong flu was one of the famous influenza pandemics in history. It was caused by an H3N2 strain of the influenza A virus, descended from H2N2 through antigenic shift, a genetic process in which genes from multiple subtypes reassorted to form a new virus. The Hong Kong Flu (1968 pandemic influenza) H3N2 Hemagglutinin (HA) proteins and antibodies were the main research tools for this influenza pandemic.
The first record of the outbreak in Hong Kong appeared on 13 July 1968. By the end of July 1968, extensive outbreaks were reported in Vietnam and Singapore. Despite the fatality of the 1957 Asian Flu in China, little improvement had been made regarding the handling of such epidemics. The Times newspaper was actually the first source to sound alarm regarding this new possible pandemic.
By September 1968, the flu reached India, Philippines, northern Australia and Europe. That same month, the virus entered California from returning Vietnam War troops but did not become widespread in the US until December 1968. It would reach Japan, 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.
The same virus returned the following years: a year later, in late 1969 and early 1970, and in 1972.
Flu symptoms lasted 4 to 5 days. Those over the age of 65 were most likely to die.
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. The pandemic infected an estimated 500,000 Hong Kong residents, 15% of the population. In the United States, approximately 33,800 people died.
Fewer people died during this Hong Kong flu pandemic than the two previous influenza pandemics for various reasons: some immunity against the N2 flu virus may have been retained in populations struck by the Asian Flu 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.