The New York Times :
Confusing test results in recovered patients fueled fears that repeat coronavirus infections were possible. Big nonprofits like the American Red Cross, lifelines in the pandemic, face drastic cuts.
Florida’s caseload has reached 423,847, surpassing New York’s count and currently behind only California, a state with nearly double its population.
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, the protective proteins generated in response to an infection.
This has led to concerns that people may be susceptible to repeat infections.The problem, 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 miss antibodies that are present at low levels.
Moreover, some tests – including those made by Abbott and Roche and offered by Quest Labs and LabCorp – are designed to detect a subtype of antibodies that doesn’t confer immunity and may wane even faster than the kind that can destroy the virus.
But the declining antibodies 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. Virtually everyone infected with the coronavirus seems to develop T-cell responses, according to several recent studies.
For now, many experts urge caution. While it appears extremely unlikely that people can be reinfected, without more information about what antibody testing results mean, they said, people should act as though they do not have immunity.
