Hong Kong Flu
Also known as: 1968 Pandemic
Overview
The Hong Kong flu pandemic of 1968–1970 was caused by an H3N2 influenza A virus that emerged in Hong Kong in July 1968. It was a reassortant strain combining the hemagglutinin from an avian virus with the neuraminidase from the previously-circulating H2N2. Partial immunity to the N2 neuraminidase from the prior pandemic probably reduced mortality relative to earlier pandemics.
The pandemic spread to the United States by September 1968 (carried largely by returning Vietnam War service members), reached Europe by Christmas, and circulated globally through 1970. An effective vaccine was not produced in time to affect the first wave but was available for the 1969 winter season.
Deaths worldwide are estimated at 1–4 million, with roughly 100,000 in the United States (most over age 65). H3N2 remains one of the four influenza A subtypes circulating as seasonal flu today.
Timeline
- July 1968Outbreak in Hong Kong.
- September 1968US cases begin arriving via returning soldiers from Vietnam.
- December 1968European epidemic peaks; vaccine not yet widely available.
- Winter 1969–70Second wave in Europe and Japan, higher mortality than first.
- 1970Pandemic ends; H3N2 becomes seasonal strain.
- PresentH3N2 continues to circulate and cause seasonal influenza.
Impact
The Hong Kong flu caused significant but less severe mortality than the 1957 pandemic, partly due to partial immunity to the shared N2 neuraminidase. It highlighted the inadequacy of existing vaccine production timelines for pandemic response and accelerated work on faster manufacturing methods. H3N2 remains a major cause of seasonal flu mortality, particularly among the elderly.
How it ended
The pandemic waned as immunity spread and vaccines became widely available. H3N2 continues circulating today as a seasonal influenza strain.
Sources
- CDC 1968 Pandemic (H3N2)
- Viboud, Cécile et al. (2005). 'Multinational impact of the 1968 Hong Kong influenza pandemic.' Journal of Infectious Diseases.