Live Global Coronavirus News: Antibody Puzzle Complicates Immunity Question

The limits of antibody testing add to the immunity mystery.

One of the great mysteries of the coronavirus pandemic has been the fact that many stricken people have later discovered that they don’t seem to have antibodies, protective proteins that are generated in response to an infection.

This has led to concerns that, without the immunity typically provided by a previous encounter with a virus, people may be susceptible to repeat coronavirus infections.

The complication, writes The Times’s Apoorva Mandavilli, lies in the antibody tests.

Most commercial antibody tests offer crude yes-no answers. The tests are notorious for delivering false positives — results indicating that someone has antibodies when they do not.

But the volume of coronavirus antibodies is known to drop sharply once the acute illness ends, and it has become increasingly clear that tests may produce false-negative results, missing antibodies that are present at low levels.

But declining antibodies, as indicated by commercial tests, don’t necessarily mean declining immunity, several experts said.

“Whatever your level is today, if you get infected, your antibody titers are going to go way up,” said Dr. Michael Mina, an immunologist at Harvard University, referring to the levels of antibodies in the blood. “The virus will never even have a chance the second time around.”

A small number of people may not produce any antibodies to the coronavirus. But even then, they will have “cellular immunity,” which includes T cells that learn to identify and destroy the virus.

“This means that even if the antibody titer is low, those people who are previously infected may have a good enough T-cell response that can provide protection,” said Akiko Iwasaki, an immunologist at Yale University.

For now, many experts urge caution. Without more information about what antibody testing results mean, they said, people should act as though they do not have immunity.

In the first wave of the outbreak, the 2,600 national outposts of the Y.M.C.A. transformed into civic centers, caring for the children of emergency medical technicians, doctors and other essential workers when day care centers closed down, as well as feeding the poor when schools that offered meal programs shut their doors.

Now the Y.M.C.A. finds itself in financial jeopardy just as it is needed most.

It sealed its borders in late January, shutting off business with neighboring China, which accounts for nine-tenths of its external trade. It clamped down on the smugglers who keep its thriving unofficial markets functioning. It quarantined all diplomats in Pyongyang for a month.

A Covid-19 outbreak could seriously test North Korea’s underequipped public health system and its economy, already struggling under international sanctions. Relief agencies have been providing test kits and other assistance to help the country fight any potential spread.

In other news from around the globe:

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Reporting was contributed by Apoorva Mandavilli, Nicholas Kulish, Michael Wilson, Adam Nagourney, Choe Sang-Hun, Jennifer Jett, Fahim Abed, Ernesto Londoño and Raphael Minder.