Antibody Tests Get a Questionable Second Life
(Bloomberg) -- When Mark Fields received test results from a routine physical last month, he got a stark surprise. Along with all the bloodwork typical for a 66-year-old man, the doctor had also ordered a Covid-19 antibody test. And though Fields had received both doses of the Pfizer vaccine months earlier, his doctor said the test results suggest his immune response to the vaccine had been low.
Fields, a New Yorker, didn’t know what to make of the information. Did he need a booster shot? Should he go back to double-masking, as he had throughout the pandemic? Was the antibody test simply wrong?
“I was worried,” he said.
Not knowing where else to turn, he tweeted at Rochelle Walensky, the director of the Centers for Disease Control and Prevention, asking her what to do. He never heard back and his doctor instructed him to simply do nothing since he was already vaccinated. Still, the episode was troubling.
Fields most likely has nothing to worry about. Approved vaccines for Covid-19 have shown to be extremely effective. Yet even the best vaccines are not 100% effective. And that has created a doubt that makers of Covid-19 antibody tests are seeking to capitalize on. For people seeking the comfort of certainty, these companies are stepping up to provide a semblance of reassurance — and sell products that haven’t been used much since the early phase of the pandemic.
Though regulators warn against using antibody tests as a predictor of a vaccine’s effectiveness, companies including Laboratory Corp of America Holding and Quest Diagnostics Inc., have been marketing to patients and medical professionals alike the idea that antibody tests can shed light on a vaccine’s effectiveness.
On LabCorp’s website, for example, it suggests its tests can check for antibodies to Covid-19 for the vaccinated — without clarifying until lower down on the page that antibodies aren’t equivalent to immunity. The company presents similarly contradictory messages in information for doctors and hospitals -- even going so far as to tie positive antibody tests with “neutralizing effects,” a signal of immunity.
On a February call with investors, LabCorp Chief Executive Officer Adam Schechter talked up the potential to sell more antibody tests as vaccines were rolled out, and said that LabCorp was preparing to expand its capabilities accordingly.
“Labcorp, through its online resources, continues to communicate that evidence is still being collected to determine the role of antibodies in protecting against SARS-CoV-2,” a company spokesperson said, calling antibody tests a key piece of information used in assessing Covid-19 patients.
A spokesperson for Quest said that the company has adjusted messaging “to conform with changing guidance from the regulatory community.” The company still says on its website that people can test positive after a Covid-19 vaccination, but notes that “the clinical significance is not yet known, nor is it known how good this test is at detecting antibodies in those who have been vaccinated.”
Roche Holding AG, meanwhile, said late last year that a new antibody test it had begun to offer, a semi-quantitative test that measures a person’s level of antibodies rather than merely assessing whether they have antibodies at all, could be used to measure a person’s vaccine response. “Antibody tests like these will play a critical role in measuring a person's vaccine-induced immune response,” Matt Sause, president and CEO of Roche Diagnostics Corporation, said in a statement at the time.
A Roche spokesman said in a statement that the “utilization of antibody tests for this explicit intended use will be based on rigorous study data, which we undertake in collaboration with our healthcare partners.”
The rub is there’s not yet sufficient research to support the notion that a person's antibody test results following a vaccine helps show whether the vaccine is working. And the Food and Drug Administration has signaled these marketing strategies may be premature.
“While a positive antibody test result can be used to help identify people who may have had a prior SARS-CoV-2 infection, more research is needed in people who have received a COVID-19 vaccination,” the FDA said in a statement last month. The medical community shouldn’t rely on antibody tests as a means of assessing immunity to the virus, particularly after Covid-19 shots, the agency said.
Commerical antibody tests were developed to measure recent infection from the virus, rather than the vaccine response. They can’t reliably establish whether a person is immune to Covid-19. While they measure antibodies, protective proteins that vaccines produce by stimulating the body’s immune system, vaccines might also provide protection via other mechanisms, like T cells. To make matters even more complicated, scientists don’t yet understand what amount of antibodies translates to protection from the coronavirus. Different tests, meanwhile, measure different aspects of infection that may not translate to the vaccine a person received.
Scientists said they’re worried about test-takers making important life decisions based on misleading data. Someone might decide not to go back to work, for example, if they believe their vaccine hasn’t provided adequate protection, or might prematurely drop all precautions if the results suggest the opposite. While the CDC has said fully vaccinated individuals can go back to pre-pandemic activities without masking or staying six feet(1.8 meters) apart, most experts say continuing to take safety measures like wearing a mask or avoiding large gatherings still makes sense in certain situations, especially in areas where infections are high.
“In the real world we’ve proved vaccines are effective in preventing disease regardless of your antibodies. But we don’t yet have the data to say how it’s working,” said Luis Ostrosky, chief of infectious diseases at UTHealth in Houston. “The key message here is don’t make life decisions based on this test.”
The confusion extends beyond lab testing offered by U.S. companies. In India, the story of a man who said he had no antibodies after receiving his Covidshield jab went viral after it was picked up by the mainstream Indian press. He filed a complaint alleging he had been defrauded. In the U.S. , the official Indiana state website says that people should test positive on an antibody test after they are vaccinated.
Test-takers also must make sure the antibody test they plan on taking is the right type. Some tests, for example, measure antibodies against nucleocapsid protein, a specific structural part of the virus. But all of the vaccines approved in the U.S. elicit an immune response only to the virus’ spike protein, which would require a different type of test. A nucleocapsid antibody test might turn out positive if you’d contracted Covid, but not if you had only been vaccinated against it.
The vast majority of people will test positive for spike antibodies after vaccination with tests targeting those specific antibodies, said Kimia Sobhani, medical director of clinical chemistry at Cedars-Sinai Medical Center in Los Angeles. Sobhani is using antibody tests in research to track responses to Covid-19 vaccines in health care workers.
But only in rare situations will antibody tests prove useful, she said. For the immune-compromised, for example, there is a far higher risk that a vaccine might not work and so an antibody test can provide useful evidence.
Additional research needs to be done to establish standards for measuring immunity and tests also need to be standardized, Sobhani and other scientists said.
©2021 Bloomberg L.P.