The volunteer was a man in his 20s, according to reports. It was not immediately clear if the man received the vaccine or had been part of a placebo group.
Last week, Pfizer Inc. received permission to test its vaccine in U.S. kids as young as 12, one of only a handful of attempts around the world to start exploring if any experimental shots being pushed for adults also can protect children.
The nation has 15,000-16,000 nursing homes, according to the Centers for Disease Control and Prevention. There may be another 20,000-45,000 assisted living facilities and similar kinds of settings for elderly and disabled people.
Pfizer Inc. cannot request emergency authorization of its COVID-19 vaccine before the third week of November.
The WHO study looked at four existing COVID-19 treatments, including remdesivir and hydroxychloroquine, and found each had "little or no effect" on a patient's survival.
Horseshoe crab blood has been used in the medical world for decades.
Regeneron is seeking emergency use authorization from the FDA for its drug that was used to treat President Donald Trump while he was hospitalized with COVID-19.