The most recent influenza pandemic occurred in 1968 with the Hong Kong Flu (H3N2) outbreak, which resulted in nearly 34,000 deaths in the United States. The 1968/69 pandemic, which was milder than 1957, is thought to have caused around 1 million deaths worldwide. In early 1968, the Hong Kong influenza pandemic was first detected in Hong Kong. It then spread worldwide during the following two winters, causing greater morbidity in some countries the first winter and others the second. The first cases in the US were detected as early as September of 1968, but illness did not become widespread in the US until December 1968. Deaths from this virus peaked in December 1968 and January 1969. Those over the age of 65 were most likely to die. The same virus returned a year later, in late 1969 and early 1970 [peaking in the UK in January 1970] and in 1972. The number of deaths between September 1968 and March 1969 for this pandemic was 33,800, making it the mildest pandemic in the 20th century.
In the 1968 pandemic vaccine became available one month after the outbreaks peaked in the US.
There could be several reasons why fewer people in the US died due to this virus. First, the Hong Kong flu virus was similar in some ways to the Asian flu virus that circulated between 1957 and 1968. Earlier infections by the Asian flu virus might have provided some immunity against the Hong Kong flu virus that may have helped to reduce the severity of illness during the Hong Kong pandemic. Second, instead of peaking in September or October, like pandemic influenza had in the previous two pandemics, this pandemic did not gain momentum until near the school holidays in December. Since children were at home and did not infect one another at school, the rate of influenza illness among schoolchildren and their families declined. Third, improved medical care and antibiotics that are more effective for secondary bacterial infections were available for those who became ill.