Most major blood groups were identified early in the 20th century. Many discovered since, like the Er blood system first described by researchers in 2022, only impact a small number of people. This is also the case for the new blood group. "The work was difficult because the genetic cases are very rare," explained Tilley.

What blood type are you? That question usually results in a response of A, B, AB or O. Then maybe a positive or negative, also called the rhesus factor. However, researchers have now identified another elusive blood group after a 50 year mystery.