SANTIAGO, CHILE — Researchers in Argentina and Chile reported that four of five hantavirus patients survived after receiving the rheumatoid arthritis drug tocilizumab during a 2025 outbreak. The treatment was administered under a compassionate use protocol linked to a cruise ship that docked in Santiago, Chile. The Andes virus, identified as the cause of this outbreak, is the only known hantavirus capable of limited human-to-human transmission, and no approved treatments or vaccines were available for passengers during the outbreak.
Three of 13 probable hantavirus cases among cruise ship passengers resulted in death. Tocilizumab, which inhibits IL-6, a molecule linked to severe inflammation and fluid accumulation in the lungs, was provided to patients in an Argentine hospital. Five additional patients deemed eligible for the compassionate use protocol who received only standard care died. Two other eligible patients deteriorated before treatment could be administered, and hospital drug supplies were insufficient for additional patients.
The published data represents the first documented use of tocilizumab for hantavirus under a compassionate use protocol, according to research published in The Lancet Infectious Diseases. The study authors concluded that tocilizumab requires additional clinical evaluation. Researchers anticipate that increased attention from the recent outbreak and climate-driven increases in human-rodent contact could advance research funding for hantavirus. Lead author Dr. Fernando Tortosa, at the National University of Río Negro, said, "I hope this situation will help us continue our research and strengthen the collaboration between healthcare workers, the community, and the necessary resources."
Hantavirus is a family of rodent-borne viruses believed to occur globally. Hantavirus infections occur infrequently but carry high mortality rates, with 35% of documented U.S. cases since 1993 resulting in death. Research teams in Chile, Argentina, and the United States have pursued the development of hantavirus drugs and vaccines. Sustained investment for safety and efficacy testing has been limited due to the low frequency of infections and limited human-to-human transmission.
The World Health Organization states that no licensed vaccines currently exist for hantaviruses. Development is underway for new hantavirus vaccines, including candidates targeting the Andes virus. Dr. Paul Bollyky, an infectious disease researcher at Stanford Medical Center, identified a lack of specialized testing infrastructure and the unpredictable nature of outbreaks as barriers to rare disease vaccine development. He said, "That also makes clinical trials in this space super difficult because of the number of people you would have to immunize to protect against one infection. It's just impractical."
María Inés Barría, a virologist at Universidad San Sebastián, said, "That is why it is a public health problem." She added, "We are truly at the forefront, at a very important stage of moving to the next phase." Dr. Tortosa added, "What happened was a tragedy, but it can happen not only with this but also other diseases."