Asian flu: A pandemic of influenza A (H2N2) in 1957-58. First identified in China in late February 1957, the Asian flu spread to the United States by June 1957 where it caused about 70,000 deaths. Also known as Asian influenza.

Immunity to this strain of influenza A (H2N2) was rare in people less than 65 years of age, and a pandemic was predicted. In preparation, vaccine production began in late May 1957, and health officials increased surveillance for flu outbreaks. Unlike the virus that caused the 1918 pandemic, the 1957 pandemic virus was quickly identified, due to advances in scientific technology. Vaccine was available in limited supply by August 1957.

The virus came to the United States quietly, with a series of small outbreaks over the summer of 1957. When children went back to school in the fall, they spread the disease in classrooms and brought it home to their families. Infection rates were highest among school children, young adults, and pregnant women in October 1957. Most influenza-and pneumonia-related deaths occurred between September 1957 and March 1958. The elderly had the highest rates of death. By December 1957, the worst seemed to be over.

However, during January and February 1958, there was another wave of illness among the elderly. This is an example of the potential "second wave" of infections that can develop during a pandemic. The disease infects one group of people first, infections appear to decrease and then infections increase in a different part of the population.