A new saliva-based test was found to accurately detect the presence of antibodies to SARS-CoV-2

reviewed by Emily Henderson, Bachelor of Science15 november 2020

A new saliva-based test developed by a team at Johns Hopkins University’s Bloomberg School of Public Health has been found to accurately detect the presence of antibodies to SARS-CoV-2, the virus that causes COVID-19, from small samples of saliva, according to a study led by researchers at the Bloomberg School. These tests, the results of which can be obtained in a matter of hours, are considered potential alternatives to antibody testing with 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 detected antibodies against several of these antigens in saliva samples from the 24 participants who had confirmed exposure to SARS-CoV-2 and whose symptoms had started more than two weeks before the test. The test also returned reliable negative results for saliva samples that had been collected from people prior to the COVID-19 pandemic.

The study appears online at Journal of Clinical Microbiology.

If the precision of our saliva-based assay is confirmed in larger studies, this non-invasive approach could facilitate the identification, at the population level, who has already had a SARS-CoV-2 infection and where gaps in seropositivity persist. into winter. and beyond. This could inform targeted vaccination efforts and, after vaccines start rolling out, help determine how long vaccine-induced antibodies last, all without repeated and invasive blood draws. ”

Christopher D. Heaney, PhD, MS, lead author of the study, associate professor with appointments in the departments of Engineering and Environmental Health, Epidemiology and International Health at the Bloomberg School

The pandemic spread of SARS-CoV-2 has officially caused more than 40 million infections and more than 1 million deaths worldwide. Many epidemiologists suspect that the actual spread of the virus has been much more extensive, but that and many other questions about the scope and dynamics of the pandemic thus far have been difficult or impossible to specifically answer. However, a relatively rapid, inexpensive, non-invasive, and high-precision antibody test could greatly facilitate research.

Heaney and his colleagues had previously invented accurate saliva-based antibody tests for other viruses that cause disease, including the enteric pathogen norovirus and the hepatitis E virus that infects the liver.

At the beginning of the pandemic, the research team developed a saliva-based test to detect antibodies against SARS-CoV-2, using a panel of 12 known viral antigens already used for blood 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 enriched with antibodies.

That the test detected antibodies to various SARS-CoV-2 antigens in saliva samples from the 24 people who had confirmed exposure to SARS-CoV-2 and whose symptoms had arisen more than two weeks prior to the test showed that the test it could be very sensitive. -that is, able to identify positive results.

The experiments also showed that the test could be highly specific, that is, able to identify those without the antibodies with a low “false positive” rate. In a set of 134 saliva samples that had been collected from people long before the COVID-19 pandemic and are therefore presumed to be free of antibodies to SARS-CoV-2, several antigens in the test gave negative results in all but a few. cases. Antibodies against a viral antigen seemed particularly specific: Scientists found negative results in all 134 pre-COVID-19 samples.

Saliva tests for SARS-CoV-2 immunoglobulin G antibodies appeared to be as sensitive and specific as blood serological tests. After SARS-CoV-2 infection, IgG antibodies generally rise around day 10 after the onset of symptoms, and these antibodies spread from the blood to the saliva.

Experiments in general have suggested that people who become infected with SARS-CoV-2 develop detectable antibodies in saliva at about the same time as they do in blood, about 10 days after the onset of COVID-19 symptoms. The researchers hope that with an optimal algorithm that integrates the results for a few especially sensitive and specific antigens, their saliva-based test can reliably detect SARS-CoV-2 antibodies starting around the same 10-day mark, but not before. .

Since submitting their paper several months ago, Heaney and his colleagues have been refining the test with experiments on thousands of more saliva samples. They hope that their saliva-based test will be useful for future research applications, especially large-scale or longitudinal studies for which invasive and potentially painful blood tests could be problematic. For example:

• Measure levels of exposure and immunity to SARS-CoV-2 in a given neighborhood, city, county, or state, or in a particular category of workers.
• Identify populations that could particularly benefit from specific vaccination campaigns.
• Monitor 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 after infection or vaccination.

The researchers also believe their test is sensitive and specific enough to have potential use in clinical settings, such as detecting previous exposures to SARS-CoV-2 before they receive a vaccine or undergo some other medical procedure.

For clinical applications, the test would need approval from the Food and Drug Administration (at least an emergency use authorization), and Heaney says that with this goal in mind, he and his colleagues are initiating discussions with the agency.