The bulls, accompanied by guiding steer, stayed together for much of the chase but one broke free toward the end, causing fear among screaming runners. An isolated bull is more dangerous because it can become disoriented and more likely to charge.
Red Cross spokesman Alfonso Contin said there were no gorings, while the city's Navarra Hospital said a 56-year-old American from New York was treated for a hand injury and a 32-year-old Spaniard suffered a broken nose.
The two were identified only by their initials. The hospital had initially said three people were injured.
The nine-day festival, made famous by Ernest Hemingway's “The Sun Also Rises,” finishes Saturday. It attracts tens of thousands of foreigners, mostly from the United States, Britain, and Australia.
In the four runs prior to Wednesday, four people—including two Britons and an American—were slightly injured in minor gorings.
In the runs, the bulls are released from a pen and herded at great speed along a narrow, winding 849-meter (928-yard) course to the city bullring. The near three-minute event is held each morning at 8 a.m. and is preceded by all-night partying in the city.
The bulls used in the centuries-old fiesta can weigh more some 600-kilogram (1320-pound) and have killed 15 people since record keeping began in 1924. The last person to die was a young Spaniard in 2009. The bulls are usually killed by matadors in evening bullfights.