False positives are erroneous results that, in this case, could lead to a conclusion that someone has immunity when he or she does not.

Researchers at the Duke-National University of Singapore Medical School said they quickly developed one antibody test that had about 90% accuracy and later introduced a more sophisticated version that was more reliable, according to a report in the Straits Times of Singapore.

Infectious disease experts say immunity against COVID-19 may last for several months and perhaps a year or more based on their studies of other coronaviruses, including Severe Acute Respiratory Syndrome (SARS), which emerged in 2003. But they caution that there is no way to know precisely how long immunity would last with COVID-19, and it may vary person to person.

“You are likely to have immunity for several months,” said Dr. Stanley Perlman, a professor of microbiology and immunology at the University of Iowa. “We just don’t know. This is an incredibly important question.”

Perlman said many of the new antibody tests coming on the market now may be highly effective, but researchers want to see data to back that up.

“You want them to be sensitive enough to detect everyone who has had the infection,” Perlman said, “but not so nonspecific that you are picking up other coronaviruses.”