The Russian flu, red influenza or red flu in 1977 was a pandemic. Many people became sick with influenza. The Soviet Union first reported it in 1977, but it may have started in China that May. Mostly people under the age of 25 became sick. About 700,000 people died. This pandemic was caused by H1N1 influenza virus, which is very similar to the virus strain that spread worldwide from 1946 to 1957.