What Pandemic Is Cause For Concern?

An influenza pandemic is a worldwide outbreak or epidemic caused by an influenza virus to which few if any humans have immunity developed by prior exposure. Influenza pandemics occur predictably but at unpredictable intervals; three occurred during the 20th century. The most serious pandemic on record, the “Spanish flu” of 1918-1919 caused an estimated 20-100 million deaths worldwide and over 500,000 deaths in the United States. Influenza viruses capable of causing a pandemic must be able to cause human disease, have novel surface antigens, and be able to spread effectively from person-to-person. Such influenza viruses can emerge through several mechanisms. Beginning in 1997 and continuing through 2007, a widespread outbreak of avian influenza (H5N1) has affected birds in multiple countries in Asia, Africa, and Europe. That strain has demonstrated the ability to cause lethal disease among humans and created concern that it might evolve into a strain of virus capable of causing a pandemic. It is not known whether that will occur, but it is certain that another influenza pandemic will afflict humans at some point in the future.