The coronavirus crept into Heartland Health Care Center, a nursing home in Moline, Ill., on the last day of July, when a member of the nursing staff tested positive.

It was an ominous sign: The virus can spread through a nursing home in a flash. Older people — who are often sick and frail and need regular hands-on attention — are uniquely susceptible. Staff members who care for residents are at high risk of infection and of unintentionally spreading the virus.

Although nursing home residents make up just 1.2 percent of the United States population, they account for about 40 percent of Covid-19 deaths.

But this time, the nursing home was not defenseless. Heartland was the first facility to participate in a large clinical trial of a drug that might protect residents from the infection in nursing homes and assisted living facilities.

A plant extract trumpeted this week as a “cure” for Covid-19 by the leader of a pillow company is untested and potentially dangerous, scientists say.

Getting an antibody test to see if you had Covid-19 months ago is pointless, according to guidelines issued this week by a major medical society.

Many tests are inaccurate, some look for the wrong antibodies and even the right antibodies fade away, said experts at the Infectious Diseases Society of America, which issued the new guidelines.

Because current tests cannot determine if someone is immune, the society said, they “cannot inform decisions to discontinue physical distancing or lessen the use of personal protective equipment.”

BEERSHEBA, Israel — A team of three Israeli scientists has pioneered a coronavirus testing procedure that they say is faster and more efficient than any now in use, testing samples in pools of as many as 48 people at once.

The Israeli government plans to roll out the new method in 12 labs across the country by October, anticipating that another wave of coronavirus infections could coincide with influenza season with potentially calamitous results. ...