The United Kingdom experiences its first critical case of A(H1N1) influenza.
- India and Turkey confirm their first cases of (A)H1N1 influenza.
- H1N1 influenza kills a third United States citizen and spreads to Australia and Japan.
- Mayor Ray Nagin of New Orleans, Louisiana, is quarantined in Shanghai, China, after a passenger on his flight from the United States was diagnosed with A(H1N1) influenza.
- The World Health Organization declares the current outbreak of H1N1 to be a "pandemic", the first since the 1968 Hong Kong flu.
- The People's Republic of China confirms its first case of (A)H1N1 influenza.