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August 24, 2022

Are you immune to Covid-19? New at-home tests may help you find out.

Daily Briefing

    Scientists are working to develop at-home tests that can determine how much protection an individual has against the coronavirus, and whether they need a booster dose—but some experts are skeptical that the tests will ever be approved for use in the general population, Edward Chen writes for STAT.

    Scientists develop at-home tests to measure protection against coronavirus

    In a new study published Monday in Cell Reports Methods, researchers presented a simple test that can detect levels of neutralizing antibodies against SARS-CoV-2 with just a finger prick and a testing cartridge.

    The test can be manufactured for under a dollar per kit. And if the method is found effective in large-scale testing and receives approval from the necessary regulatory agencies, it could provide a simple, inexpensive testing option to measure protection against the coronavirus.

    "People want to know, 'Am I protected today?' And there isn't a tool on the market that can facilitate that answer," said Charles Mace, a chemist at Tufts University who was not involved in the study. "This has that potential."

    To determine whether a person has neutralizing antibodies, scientists must take blood samples, separate the serum, and mix it with the SARS-CoV-2 virus. Then, they incubate the mixture with a human cell line and record the number of cells that die. Since this method requires the live virus, it must be conducted in a lab, which takes roughly two days to complete.

    While researchers have been developing alternative methods that are faster, most of them still require lab equipment or are difficult to manufacture because they use antibodies.

    However, in the new study, researchers "learned new techniques to make every component of a test, from producing viral proteins at a larger-scale to cycling through a hundred different buffer formulas" before they were able to design and validate the test, Chen writes.

    According to Chen, the new testing device closely resembles existing rapid antigen tests. Through a finger prick, the test draws a small amount of blood that is mixed with a buffer containing part of the SARS-CoV-2 spike protein.

    While typical antigen tests have two binding sites—one control line that demonstrates the test is working and one test line that indicates a positive test result—the new test has three binding sites, which include a control line, a line that turns red if a person does not have neutralizing antibodies, and a line that simply appears if they do.

    "We also like people to think about positive signals as opposed to reduction of signals because there's just a general feeling that that's more reliable," said Angela Koehler, a bioengineer at MIT who helped develop the new test. According to the researchers, indicating the presence and absence of neutralizing antibodies would give everyday consumers the ability to determine their antibody levels. 

    "If you have an actual number that you can measure—and neutralizing antibody concentration would be a number that you can actually measure—then you can tell what degree of protection they have and whether or not they might need a subsequent [dose] or a booster sooner rather than later," said Hojun Li, a hematologist and investigator at the Koch Institute.

    In particular, Chen notes that this kind of information would be helpful for individuals with weaker immune responses, like many of the patients Li sees. "The vast, vast majority of patients I see get bone marrow transplants," Li said. "Their immune system is just really wiped out."

    Some experts remain skeptical that the tests will be used by the general public

    Julio Delgado, the clinical pathology chief at the University of Utah School of Medicine, remains skeptical that the new test will be used by the broader population.

    "Even if I get vaccinated, I'm still going to get infected at some point. That happened to me. So the understanding about neutralizing antibodies has really become more of a scientific interest, not necessarily a clinical utility," said Delgado, who has developed lab-based clinical tests that measure levels of antibodies against the virus.

    In addition, some experts said that any use case is too optimistic since researchers still do not know what antibody levels provide optimal protection.

    "There is not an understanding about thresholds above or below which people are going to be prone to getting infected, or prone to develop progressive disease, or prone to die," Delgado added. "Yes, you get a number, but what does that mean?"

    The test's developers said their new product may be able to answer that question.

    Hadley Sikes, a chemical engineer at MIT and a senior author of the research, said, "If there was a study design where you use this tool—you recruit a cohort, say, 5,000 or 10,000 people, you get these neutralizing antibody tests in their homes, and you follow who gets infected and doesn't get infected—it's an answer to a question that a lot of people, a lot of doctors, a lot of articles in the press have been raising." (Chen, STAT, 8/23)

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