The veneration of relics is an age-old tradition in the Church, and no, we do not worship them as some people might think. It is a tradition going back to the early days of the Church to venerate them as reminders of the holiness of these great Christians. As the originator of World Youth Day, John Paul II obviously had a great connection to this event. A vial of his blood was sent to World Youth Day in Madrid in 2011 and has again been sent to World Youth Day in Rio to be venerated by the faithful.
This vial arrived in Rio in early July and will remain in Rio for several weeks after World Youth Day officially ends on July 28th so that visitors and locals alike will have the opportunity venerate his relic.
Among other relics at WYD in Rio are the body of Blessed Pier Giorgio Frassati, St. Thérèse of Lisieux, Blessed Chiara Luce Badano, Blessed Frédéric Ozanam and St. Antônio Galvão de Santana, the first Brazilian-born Saint.