But in fine print, a warning required by the U.S. Food and Drug Administration on some of these tests is blatant: negative results do not exclude SARS-CoV-2 and positive results may be false. State public health officials have also warned that it is not yet known whether specific positive results mean protection against future infection.
The warnings show the challenge faced by Governor Gavin Newsom and other leaders as they try to lift restrictions and revive economic activity amid the COVID-19 pandemic: the technology needed for one of the most critical elements of their plan is still unproven.
“There is a lot of hype about antibodies, but we don’t even know for sure if antibodies boost long-term immunity in this disease,” said Dr. Ed Thornborrow, senior medical director of the clinical laboratories at ‘UCSF. “There is still a lot of work we need to do to get there, if you are positive for an antibody test, you are immune and OK to go back to work. “
There are encouraging signs, especially with laboratory tests like that of Abbott, who received clearance from the FDA as part of the agency’s emergency use clearance process. Test results from Abbott and other laboratories have returned false positive rates as low as 0.1% – a key measure of the accuracy of a test to indicate whether people have been exposed to the virus.
The FDA also cracked down on sales of unauthorized coronavirus antibody tests on Monday, forcing companies to submit performance data proving their accuracy or to have their products withdrawn from the market. This decision follows reports from a team of Bay Area scientists and doctors and the National Institutes of Health that a significant number of commercial tests have been giving poor results since the FDA approved the drug in March. sale of antibody tests without prior authorization.
As of Friday, 12 tests had received emergency clearance from the FDA, which implies a lower standard than the usual approval procedure. The agency said it is examining more than 200 additional tests.
In the meantime, antibody tests have become increasingly available to the public in the past week alone.
Quest Diagnostics, which has 2,200 patient service centers across the country, now sells antibody tests for around $ 130 per test on the company’s website. Applications are examined by a team of doctors. If approved, a person can then go to a service center for a blood test with the results to come one to two days after. Similarly, on Wednesday, GoHealth Urgent Care – one of the largest emergency care companies in the country – began allowing the public to schedule online appointments for antibody testing at its Dignity Health centers -GoHealth Urgent Care.
But there is still a long way to go to prove the very viability of authorized antibody tests, and whether they can be used to determine immunity. For now, scientists and public health officials have said that the best use for antibody testing is in population studies that try to determine how far the virus has spread, how it continues to spread and how protective the antibodies really are by tracking individuals and taking overtime samples.
In the Bay Area, public health officials have told The Chronicle they are taking a wait-and-see approach, with some going as far as recommending that individuals not be tested – unless they are part of a population study – because of the uncertainty about accuracy and what even precise positive results could mean.
“The idea of testing resonates with people, but from a standpoint of individual use, the test doesn’t make a damn difference right now,” said Dr. Bela Matyas, public health officer at Solano County, adding that it is premature and potentially risky for companies to sell antibody tests as a comfort measure.
“The concern is that people will test positive, think they are immune and will not follow proper precautions and will not be exposed or spread the virus to others,” he said.
Although antibodies suggest immunity, scientists are yet to know which antibodies could protect, what level of antibody a person might need to be immunized, and how long an eventual immunity might last.
Antibodies are one of the main weapons of the immune system against viruses, bacteria and other pathogens. Following an infection, the body forges these specific proteins to eliminate the current infection and protect itself from future infection with the same pathogen.
Sometimes, like measles, antibodies provide lifelong protection. Other times, as with cold-storing coronavirus strains, antibodies are less effective after just one to three years.
Doctors have used antibody tests for decades to determine whether people are immune to illnesses like measles or chickenpox from vaccines or infection. For these tests, a patient’s blood is drawn and then the plasma or serum is analyzed for antibodies. The current difficulty in finding a precise and useful anti-coronavirus antibody test, however, is unprecedented in modern history in terms of speed and scale, said Jason Cyster, UCSF immunologist.
“It appears that the number of tests that have already been developed for this exceeds anything that has been done for an existing infection,” said Cyster. “But quality control takes time. “
The main challenge in developing a SARS-CoV-2 test is to determine whether the antibodies reported in a given test actually indicate immunity against future infection and, if so, to what extent and for how long. How long.
While antibodies provide some protection, it is not clear whether a person could still become infected and become contagious, which increases the possibility of people subject to return to society who can carry and spread the virus, a said Eva Harris, an infectious disease expert from UC Berkeley.
“I’m petrified of this prospect,” said Harris. “Everyone wants these answers yesterday, but science itself cannot go so fast. “
Harris is part of the effort to get some of these answers. Harris and UC Berkeley epidemiologist Lisa Barcellos on Tuesday sent leaflets to residents of 11 cities in East Bay, launching a month-long study that will repeatedly track and test thousands of people in the Bay of East Bay to get a better idea of how asymptomatic infection and disease prevalence changes as social distancing measures are lifted and if people who have antibodies can be re-infected.
But the incredibly low incidence of the infection in the bay area – some scientists believe it can be as low as 1% – means that the antibody tests for these studies must be very precise to detect the few people infected and then developed antibodies.
Local scientists and researchers are now turning to more than one test, sometimes in combination, for more precise results.
“This is a big problem,” said Harris. “The tests there have only been validated for sick people, but most of the people that these prevalence surveys will measure were not sick or had a mild illness. “
To detect as many true positives as possible, the Harris team will analyze all of its samples using two different antibody tests. Likewise, a large-scale study by Stanford and UCSF will also run all of its positive results through two different antibody tests that use different parts of the virus, making a sample that turns out to be positive for both much less likely to be a mistake.
“We want to find the positives, which means we need to look more closely for them and test more,” said Dr. Yvonne Maldonado, Stanford study co-leader and epidemiologist and infectious disease specialist.
Meanwhile, the warnings and cautions have not dissuaded people from looking for antibody tests and health care centers and test sites to sell them.
Dr. Alexa Bisinger, California medical director of Dignity Health-GoHealth Urgent Care, said that within hours of offering antibody tests to the public on Wednesday, hundreds of appointments had been booked in the bay area.
During the health crisis, the company said there would be no reimbursable costs for patients networked with commercial insurance. Dignity Health-GoHealth Urgent Care takes the blood for the antibody test and then sends the blood to Quest for the test. Quest then bills the patient for laboratory services.
GoHealth Urgent Care also provides testing to companies that may want to incorporate it into their return to work programs.
Bisinger said that health care providers will explain the limitations of the tests to patients and that the aggregated data will be shared with public health agencies and researchers to give them a better idea of the prevalence of infections.
“At the individual level, demand appears to have been turned back and exploding,” said Bisinger. “I think people want reassurance and they want hope.”
This is in part what has led many people to look for antibody tests. But often the results end up raising more questions than they answer. Some who fell seriously ill earlier this year with COVID-like symptoms – persistent fevers and shortness of breath – still have a negative result, while others with whom they live have tested positive.
Marin County public health officer Dr. Matt Willis said he received numerous emails from the public and friends who wanted to test for antibodies because they suspected they might have the coronavirus. But Willis said the low incidence of infection in the area means they probably haven’t.
“I tell them you will probably be negative,” said Willis. “And that means you haven’t been infected, or you have been infected and it’s wrong. “
Willis knows the results of inconsistent antibodies from personal experience. After he and a family member were sick in March and tested positive for the coronavirus, he also wanted to see if they had developed antibodies.
However, only Willis initially returned as having antibodies in tests they performed at a local clinic. However, after another week, the family member had another test and returned positive too.
“Everyone’s immune system is different and this can lead to different results,” said Willis. “So what it told me was that there are a lot of things we still don’t know. “
Cynthia Dizikes is a writer for the San Francisco Chronicle. Email: [email protected] Twitter: @cdizikes