The woman, who has only been identified by her initials, J.E., underwent emergency surgery after being gored in the back, according to the Telegraph. J.E. reportedly suffered multiple rip fractures and lung damage and officials said her condition was very grave.
The incident took place on the last day of the multi-day event, in which panicked bulls run down the crowded streets of Pamplona, a tradition that dates back to the 16th century.
Four other runners suffered relatively minor injuries on the festival's final day, a marked difference from Saturday's run, in which a 23-person pile-up sent five people to the hospital.