Resumen: The study of social contagion processes is of utmost importance for understanding the emergence of collective social states. Here we introduce reinfections in the Susceptible-Infected-Recovered (SIR) model so to incorporate the possibility that an individual that ceases its activity (recovered) can resume it due to secondary infections from its active (infected) peers. We show that, when primary infection is less frequent than secondary ones, a typical situation in many social contagion processes, the epidemic transition turns from smooth to abrupt. As a consequence, macroscopic collective states can be triggered from the inactive (healthy) regime by a small increment of the primary contagion rate. Idioma: Inglés DOI: 10.1209/0295-5075/110/58006 Año: 2015 Publicado en: Europhysics letters 110, 5 (2015), 58006 [5 pp.] ISSN: 0295-5075 Factor impacto JCR: 1.963 (2015) Categ. JCR: PHYSICS, MULTIDISCIPLINARY rank: 19 / 79 = 0.241 (2015) - Q1 - T1 Factor impacto SCIMAGO: 0.625 - Physics and Astronomy (miscellaneous) (Q2)