1968 Pandemic (H3N2 virus)
The 1968 pandemic was caused by an influenza A (H3N2) virus comprised of two genes from an avian influenza A virus, including a new H3 hemagglutinin, but also contained the N2 neuraminidase from the 1957 H2N2 virus. It was first noted in the United States in September 1968. The estimated number of deaths was 1 million worldwide and about 100,000 in the United States. Most excess deaths were in people 65 years and older. The H3N2 virus continues to circulate worldwide as a seasonal influenza A virus. Seasonal H3N2 viruses, which are associated with severe illness in older people, undergo regular antigenic drift.
https://www.cdc.gov/flu/pandemic-resources/1968-pandemic.html
The Hong Kong flu (also known as 1968 flu pandemic) was a category 2 flu pandemic whose outbreak in 1968 and 1969 killed an estimated one million people all over the world. 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 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.
By September 1968, the flu reached India, the Philippines, northern Australia, and Europe. That same month, the virus entered California from returning Vietnam War troops but did not become widespread in the United States until December 1968. It would reach Japan, Africa, and South America by 1969. The outbreak in Hong Kong, where population density is greater than 6,000 people per square kilometre, reached maximum intensity in two weeks, lasting six months in total from July to December 1968. However, worldwide deaths from this virus peaked much later, in December 1968 and January 1969.
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.
The same virus returned the following years: a year later, in late 1969 and early 1970, and in 1972. The CDC currently estimates that, in total, the virus killed 1 million people worldwide and around 100,000 people in the U.S.
https://en.wikipedia.org/wiki/1968_flu_pandemic
https://www.britannica.com/event/Hong-Kong-flu-of-1968
