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It was found that a new saliva-based test developed by a team at the Johns Hopkins Bloomberg School of Public Health accurately detects the presence of antibodies to SARS-CoV-2, the virus that causes COVID-19, from small saliva samples. according to a study by Bloomberg School researchers. Such tests, the results of which can be obtained within hours, are seen as potential alternatives to antibody tests on blood samples for research and clinical use.
The test is based on multiple fragments, or “antigens,” of the SARS-CoV-2 coronavirus, primarily from its outer peak and nucleocapsid proteins. In the study, the researchers found that their test found antibodies to many of these antigens in the saliva samples of all 24 participants who had confirmed exposure to SARS-CoV-2 and whose symptoms had started more than two weeks earlier. of the test. The test also reliably produced negative results for saliva samples that had been collected from people before the COVID-19 pandemic.
The study appears online in Journal of Clinical Microbiology.
“If the accuracy of our saliva-based dosing is confirmed by larger studies, this non-invasive approach could make it easier to identify, at the population level, who has already had a SARS-CoV-2 infection and where gaps in HIV positive they remain winter and beyond, ”says senior study author Christopher D. Heaney, PhD, MS, associate professor with positions in the departments of environmental health and engineering, epidemiology and international health at Bloomberg School. “This could inform targeted vaccination efforts and, after vaccines start rolling out, help understand how long vaccine-induced antibodies last – all without repeated and invasive blood draws,” Heaney says.
The pandemic spread of SARS-CoV-2 has officially caused over 40 million infections and over 1 million deaths worldwide. Many epidemiologists suspect that the actual spread of the virus has been much more extensive, but so far it has been difficult or impossible to specifically answer this and many other questions about the magnitude and dynamics of the pandemic. However, a relatively quick, inexpensive, non-invasive, and highly accurate antibody test could make that search much easier.
Heaney and colleagues have previously invented accurate saliva-based antibody tests for other pathogenic viruses, including the enteric pathogen norovirus and the hepatitis E virus.
Early in the pandemic, the research team developed a saliva-based test for SARS-CoV-2 antibodies, using a panel of 12 known viral antigens that are already being used for blood-based antibody tests. Saliva samples for testing are collected by rubbing a sponge between people’s teeth and gums, where saliva is known to be particularly rich in antibodies.
That the test detected antibodies to various SARS-CoV-2 antigens in saliva samples from all 24 people who had confirmed exposure to SARS-CoV-2 and whose symptoms had arisen more than two weeks before the test showed that the test could be very sensitive – that is, capable of identifying positive results.
The experiments also showed that the test could be highly specific, meaning it can identify those without the antibodies with a low rate of “false positives”. In a series of 134 saliva samples that had been collected from people long before the COVID-19 pandemic – and thus assumed to be free of SARS-CoV-2 antibodies – several antigens in the test gave negative results in all but a few. cases. Antibodies to a viral antigen appeared to be particularly specific: scientists found negative results for it in all 134 pre-COVID-19 samples.
The saliva-based test for immunoglobulin G antibodies against SARS-CoV-2 appeared to be just as sensitive and specific as the blood-based serological tests. After SARS-CoV-2 infection, IgG antibodies typically rise around day 10 after the onset of symptoms, and these antibodies pour from the blood into saliva.
The experiments overall have suggested that people who become infected with SARS-CoV-2 develop detectable antibodies in their saliva around the same time they do in their blood, about 10 days after the onset of COVID-19 symptoms. The researchers expect that with an optimal algorithm that integrates results for only a few particularly sensitive and specific antigens, their saliva-based test will be able to reliably detect SARS-CoV-2 antibodies starting at the same sign as 10 days, but not earlier.
Since submitting their paper several months ago, Heaney and colleagues have perfected the test with experiments on thousands of other saliva samples. They expect their saliva-based testing to be useful for future research applications, particularly large-scale or longitudinal studies for which invasive and potentially painful blood-based testing could be problematic. For example:
- Measurement of exposure and immunity levels to SARS-CoV-2 in a particular neighborhood, city, county or state or in a particular category of workers.
- Identification of populations that could particularly benefit from targeted vaccination campaigns.
- Track changes in antibody positivity rates over time to help evaluate government or corporate risk reduction campaigns.
- Determine how long antibody levels persist in large populations following infection or vaccination.
The researchers also believe their test is sensitive and specific enough to have potential use in clinical settings, such as screening individuals for previous exposure to SARS-CoV-2 before receiving a vaccine or undergoing some other medical procedure.
For clinical applications, the test would require Food and Drug Administration approval – at least authorization for emergency use – and Heaney says with that goal in mind he and his colleagues are initiating discussions with the agency.
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“Population Scale COVID-19 Serology: Specific Antibody Responses for SARS-CoV-2 in Saliva” was written by Nora Pisanic, Pranay Randad, Kate Kruczynski, Yukari C. Manabe, David L. Thomas, Andrew Pekosz, Sabra L . Klein, Michael J. Betenbaugh, William A. Clarke, Oliver Laeyendecker, Patrizio P. Cateregli, Benjamin Larman, Barbara Detrick, Jessica Fairley, Amy Sherman, Nadine Rouphael, Srilatha Edupuganti, Douglas Granger, Steve Granger, Matthew Collins and Christopher D . Heaney.
Research support was provided by the Johns Hopkins COVID-19 Research Response Program, the FIA Foundation, the GRACE Communications Foundation, the National Institute of Allergy and Infectious Diseases (R21AI139784, R43AI141265, R01AI130066, HHS N2772201400007C), National Institute of Environmental Health Sciences (R01ES026973) and National Institutes of Health (U24OD023382).
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