Jose Garrido and colleagues have isolated antibodies from human survivors of Andes hantavirus (ANDV) infection that protected hamsters against the deadly disease. The antibodies shielded the animals even when administered after infection, suggesting they could be used as a post-exposure preventative treatment for a disease that currently has no curative options. Hantavirus infections, which are transmitted from rodents to humans, are a major concern due to their high mortality rates. ANDV infection results in an extremely dangerous condition known as hantavirus cardiopulmonary syndrome (HCPS), which can cause fever, headache, low blood pressure, and heart and lung failure. The ANDV virus - the primary cause of HCPS cases in South America - is the only hantavirus that can be transmitted from person to person. Several studies in humans have shown that the generation of neutralizing antibody responses strongly correlates with survival from HCPS. Suspecting that antibodies from former HCPS patients who had survived infection could be exploited as therapeutic agents, Garrido et al. examined serum samples from 27 HCPS Chilean patients and screened how well their antibodies neutralized ANDV. They identified one patient with particularly promising ANDV neutralizing activity, isolated the patient's memory B cells, and studied two antibodies named MIB22 and JL16 that recognized and neutralized ANDV. Both antibodies prevented HCPS following administration in 100% of hamsters that had received a lethal dose of HNDV three days prior, indicating they could form the backbone of an HCPS treatment either separately or combined, the authors say.