ZURICH/GENEVA : The World Health Organization on Monday was cautious about endorsing the use of recovered COVID-19 patients' plasma to treat people who are ill, saying evidence it works remains "low quality" even as the United States issued emergency authorization for such therapies."There are a number of clinical trials going on around the world looking at convalescent plasma compared to the standard of care," Soumya Swaminathan, WHO chief scientist, said."Only a few of them have actually reported interim results...and at the moment, it's still very low-quality evidence," she told a news conference.