As New York Begins ‘Aggressive’ Antibody Testing, Experts Caution Much Still Unknown About Immunity

Over the weekend, New York Gov. Andrew Cuomo announced that his state would be the first to roll out a large-scale campaign to test the state’s residents for antibodies to coronavirus. The idea is to get a clearer picture of how many people have been infected—including those who didn’t show symptoms—and arm them with information about their possible immunity to the virus. 

But while many state and local leaders have placed hope in widespread antibody testing as a key step to relaxing social distancing measures and restarting the economy, public health officials at the World Health Organization warn that too many of the test results may be inaccurate. They also caution that much is still unknown about immunity to the coronavirus even for people who were diagnosed and recovered from the respiratory illness. 

Cuomo said that the state will start by testing 3,000 people this week, a measure that will give officials “the first true snapshot” of the spread of coronavirus in the state. “We don’t really know how many people were infected … We don’t really know because we haven’t been able to do testing on that large of a scale,” Cuomo said. “We’re going to do that in the most aggressive way in the nation. We’ll have the first real statistical number on exactly where we are as a population.” 

The daily death toll in New York dropped on Monday to 478, the first time the number has been below 500 since April 2. The state has confirmed 242,817 cases as of Monday, the most of any state by a significant margin.

Those case numbers are likely undercounts of the actual number of people infected by the novel coronavirus. Doctors at New York-Presbyterian/Columbia University Irving Medical Center this week published a study about their move to implement universal screening for Covid-19 among labor and delivery patients. The findings showed that about 15% of patients tested positive for the virus, but 88% of those infected had no symptoms. “Our screenings suggest more people are infected with the virus but are not becoming sick,” the doctors wrote.

Asymptomatic carriers may be spreading the virus to others without knowing it. The idea behind antibody tests is that a blood screen will identify these people, as well as showing what level of resistance—the antibodies they developed in fighting off Covid-19—is still present in their bodies. 

After the period of contagion, people with antibodies could be immune and, therefore, return more freely to work. They could even receive “immunity cards” that allow them greater freedom. But leaders at the WHO, like Dr. Maria Van Kerkhove, head of the emerging diseases unit, are warning against placing faith in antibody tests to determine immunity. “What the use of these tests will do will measure the level of antibodies. It’s a response that the body has a week or two later after they’ve been infected with this virus,” she said at a news conference last Friday. “Right now, we have no evidence that the use of [an antibody] test can show that an individual is immune or protected from reinfection.” 

Dr. Mike Ryan, the executive director of WHO’s emergencies program, further cautioned that scientists are still working to figure out how long someone with antibodies will have some immunity  to the virus, and whether they can be reinfected after they recover. “Nobody is sure whether someone with antibodies is fully protected against having the disease or being exposed again,” he said. 

Some scientists, though, have pointed out that getting over a virus does typically give a person some immunity to the disease. The question is for how long, as viruses can mutate. Dr. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, has said that it is reasonable to assume somebody will be protected for some period of time if they have recovered from an infection. But on Monday, Fauci, too, raised a note of caution about antibody tests, saying the ones currently on the market need to be “validated and calibrated.”

Faulty tests became the subject of intense scrutiny this weekend as reports revealed that the Food and Drug Administration authorized 90 companies to sell antibody tests in the U.S. market without reviewing them first. Many of the tests come from China and some were being fraudulently marketed as diagnostic tests that can show whether somebody is infected, experts say. Even when not improperly used for diagnosis or treatment, the antibody tests also can vary in quality, with other countries determining rapid tests too often produced false results, the New York Times reported.

In a statement released Saturday, FDA Commissioner Dr. Stephen M. Hahn said that there is “still a great deal about Covid-19 immunity that we don't yet fully understand” but that antibody testing is still useful as states make decisions about easing restrictions on daily life. “Antibody tests—also known as serological tests—may have the potential to play a role in this complex calculation,” Hahn said. “We do expect that data from more widespread serological testing will help us track the spread of the virus nationwide and assess the impact of our public health efforts now, while also informing our Covid-19 response as we continue to move forward.”

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