The H1N1 pandemic, also known as the swine flu pandemic, occurred in 2009 and was caused by a new strain of the H1N1 influenza virus. It spread rapidly around the world, leading the World Health Organization to declare it a pandemic in June 2009. The virus primarily affected younger populations, unlike typical seasonal flu strains that often impact older adults more severely. The pandemic resulted in millions of infections globally, with varying severity. Vaccines were developed and distributed to help control the spread of the virus. By August 2010, the H1N1 pandemic was declared over, but the virus continues to circulate as a seasonal flu strain.