In 1940, Thomas Francis, Jr, MD isolated the influenza B virus from a child in 1940.

Francis helped develop an inactivated vaccine effective against both influenza A and B that was successfully used to protect the U.S. military forces during World War II and directly saved more than 1 million lives.

During World War 1, the human influenza virus had dealt the armed forces a huge blow, and the epidemic that followed shortly after claimed 20 million lives..