As some states ease their closures, there is growing interest in antibody tests that can tell if you’ve been infected with the new coronavirus – and presumably, have developed some degree of immunity to the disease.
But these tests have limits, scientists warn. Of 14 antibody tests on the market, only three have provided consistently accurate results, according to an analysis carried out last month by researchers in California. as reported by the New York Times. Moreover, experts do not know how long the immune protection lasts with this new coronavirus.
Antibody tests are useful right now from a public health perspective, to determine what percentage of a population has been exposed to the novel coronavirus. They may be less significant at the individual level. The accuracy of a test depends on a number of factors, including its quality and the location of the person being tested.
Even with an accurate test, a positive antibody result is not a free pass to re-enter unrestricted daily life, scientists say. “I wouldn’t advise people, even with positive antibody tests in hand, to go back to their normal routines without thinking about social distancing,” says Daniel Larremore, assistant professor in the computer science department and the BioFrontiers Institute at the University of Colorado, Rock.
What is the antibody test?
Antibodies are proteins that attack foreign invaders in the body. The presence of antibodies to SARS-COV 2 (the virus that causes COVID-19 disease) in your blood would indicate that your immune system has been battling the new coronavirus. Antibody tests are usually done through a blood test after a person has recovered, while a nasal swab is used to diagnose an active coronavirus infection.
The accuracy of an antibody test depends on two factors: sensitivity and specificity. The sensitivity assesses whether the test can detect the antibody if it is present, and the specificity assesses whether the test can distinguish antibodies to SARS-VOC 2 from antibodies to the six other known coronaviruses, including some of the viruses that cause a cold.
A 95% specific test will give false positives 5% of the time. That is to say that in 5% of cases, it signals the presence of antibodies when there really isn’t any. False positives are more likely in places where the new coronavirus has not been spread. In a population of 1,000 people, if 1% of people have been exposed to the coronavirus, an antibody test with an accuracy of 95% will give 50 false positives and only 10 true positives. So only 1 in 6 people, or 16.6%, of people who test positive would actually have antibodies, according to a calculation for Money by Marm Kilpatrick, a professor who studies infectious diseases at the University of California at Santa Cruz.
But the results look different in a place like New York, the epicenter of the pandemic, where preliminary data from last month revealed that around 21% of residents had tested positive for antibodies. With this level of population exposed, in a test with 95% accuracy, there would be 210 people who would be true positives and 50 false positives, so 80.7% of people who tested positive would actually have antibodies.
How much does an antibody test cost?
The Trump administration demanded group and individual health insurance to cover both COVID-19 diagnosis and antibody testing without cost sharing for patients. So you may be able to get an antibody test for free, even if you haven’t reached your plan deductible for the year. That said, your health insurance plan may have a list of facilities approved for antibody testing, and if you visit one that is not on the list, you could incur additional charges.
Quest Diagnostics recently began selling antibody tests directly to the public for $ 119, plus an additional lab fee of $ 10.30. The company uses two testing platforms: one has a specificity of 98.5-99%, while the other has a specificity of 99.4%, a spokesperson told Money in an e- mail. The lower number, 98.5%, gives a 1.5% chance of a false positive. It may seem small, but in areas where a single-digit percentage of the population is exposed to COVID-19, it could cause up to half of all positives to be false positives, Kilpatrick says.
“We are committed to performing high quality testing,” a Quest spokesperson replied in an email to Money, noting that the company had performed its own quality verification tests, and that the two tests qu ‘she proposed and their performances are listed on this FDA website for authorized tests.
Where can you buy an antibody test for COVID-19
If you have private insurance, call your insurer before getting tested to be directed to an approved testing center. Many emergency care clinics now offer antibody testing, but you want to make sure you go to a place that your plan recognizes. Quest Diagnostics offers tests directly to the public online, which can be purchased without going through health insurance. After purchasing one, you go to a Quest facility to have your blood drawn.
The demand for antibody testing has attracted opportunists, Reuters recently reported. Some companies with no medical training have rushed into the market and are developing their own tests, taking advantage of federal oversight that was relaxed during the public health emergency. Consumers should investigate the accuracy of any tests they consider, experts warn. A 95% might get you an A in school, but an antibody test with that specificity isn’t the best, especially in an area with a low prevalence of the novel coronavirus.
How can states and employers use antibody testing to safely reopen?
Some governments are hoping that widespread antibody testing can help people get back to work, as the closures cripple the economy and cripple citizens’ morale. Countries, including the United States, have looked into the concept of so-called “immunity passports,” which people with antibodies would wear to allow them to resume normal life without restrictions.
But there is a risk in this strategy, scientists warn. People who receive a false positive could stop social distancing and other protective measures and put themselves and others at risk if they end up contracting the coronavirus.
Additionally, immunity passports could cause some people – such as those who cannot afford to stay at home and cannot work remotely – to actively search for infection so they can end up with antibodies. coveted, according to Alexandra L. Phelan, of the Center for Global Health Science and Security, Georgetown University Medical Center, in a recent Lancet article.
Even in the case of a true positive, it is not known how long the immunity against this new coronavirus lasts. While there have been no known cases of reinfection, we could eventually see people catching the novel coronavirus for the second time as immune protection wanes, Kilpatrick says. His best guess, based on data from other coronaviruses, is that immunity against COVID-19 can last between one and four years after infection. If a vaccine is developed within this time frame, people who have had the virus once may never get it again.
One useful way to use the most accurate antibody tests right now might be through high-risk industries, says Kilpatrick. (The pharmaceutical company Roche recently announced a test with a specificity greater than 99.8% and a sensitivity of 100%.) For example, a hospital could offer the tests anonymously to all of its nurses and allow those with antibodies to volunteer in the COVID-19 ward, knowing that some of those results could be false positives. Or a grocery store could test all employees and allow those with antibodies to volunteer to be placed at the checkout, while those without one might prefer to work on the reserve where they have no contact with them. the public.
The best way to use immunity passports would be on the basis of vaccination, says Kilpatrick. Of course, there is no way to do it now, as there is no vaccine for COVID-19. But if scientists succeed in developing one, an immunity passport based on it would reward people for their protection and that of their communities.