The influenza virus causes one of the world’s most serious respiratory illnesses. It is potentially fatal and infects humans in the tens of millions each year. The virus changes each year – sometimes a little, sometimes a lot. Major changes, known as subtype changes, produce worldwide epidemics called pandemics. In 1918, the influenza A virus subtype H1N1, known as the “Spanish Flu,” killed 500,000 people in the U.S. and 20 million people globally. In 1957, the “Asian Flu” (H2N2) killed 70,000 in the U.S., and in 1968, the “Hong Kong Flu” (H3N2) caused another epidemic. The minor changes are called strain changes, but they are not always so minor. In the 1997-1998 flu season, the “A/Sidney” strain caused almost double the U.S. yearly average of 20,000 influenza-related deaths. These yearly changes demand yearly vaccine alterations.
The next pandemic can occur at anytime. It will be a different virus subtype, one that may never have been encountered by humans. Because we will have no immunity, it will kill many more than the yearly average of 20,000 people in the U.S. Even young healthy adults will have a severe illness.