Viral hepatitis is a very common infectious disease responsible for causing more than 1.5 million annual deaths among afflicted patients. Despite the fact that extensive data reports on viral hepatitis have been first established at the beginning of the 20th century, the causes of the disease remained unknown until the 1940s, when the implication of a new virus in triggering the disease was first revealed. Performing additional research on hepatitis, virologists have later discovered two major distinctive types of hepatitis: hepatitis type A and hepatitis type B. Concerned by the increasing numbers of hepatitis cases due to blood transfusions, medical scientists have conducted a series of more elaborate medical investigations in order to identify conclusive facts regarding the occurrence and progression of hepatitis.

Intrigued by the fact that increasingly larger numbers of persons who received blood transfusions experienced symptoms such as high fever, chills and skin rashes, doctors decided to carefully analyze a series of immune reactions to foreign proteins in blood samples taken from such persons in order to reveal the exact sources of their symptoms. After comparing the immune reactions of the persons who had been administered blood transfusions with those of people in good health, medical scientists were able to reveal a type of protein that rarely reacted with antibodies produced by the immune system.

Due to the fact that the analyzed immune reaction was extremely rare, medical scientists concluded that it wasnâ ™t caused by genetic particularities in the human blood, but by a certain type of infectious agent. The discovered infectious agent later received the name of antigen Aa. After continuing their research on blood proteins, doctors discovered a correlation between antigen Aa and hepatitis. Researchers later concluded that antigen Aa was actually a component part of the virus identified to cause hepatitis B.