What Major influenza pandemics have occurred since the late 19th century?

Since the late 19th century, there have been several major influenza pandemics, including the 1918 H1N1 pandemic, also known as the Spanish flu, which resulted in millions of deaths worldwide. The Asian flu pandemic in 1957, caused by H2N2, led to significant mortality, particularly among the elderly. The Hong Kong flu in 1968, caused by H3N2, also resulted in substantial fatalities. More recently, the H1N1 pandemic in 2009, often referred to as the Swine Flu, emerged and spread globally, though it generally had a lower mortality rate than earlier pandemics.