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Saliva-based testing as a way to monitor herd immunity against SARS-CoV-2 infection

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Researchers in the United States have found that saliva-based sampling is accurate and non-invasive in blood sampling to monitor the antibody response of people after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or vaccination. It has been shown that it may serve as an alternative alternative. Virus.

The SARS-CoV-2 virus is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic and continues to pose a threat to global public health, killing more than 2.66 million people worldwide. doing.

Christopher Heaney and colleagues at Johns Hopkins University in Baltimore evaluated the durability of immunoglobulin G (IgG) antibodies against three SARS-CoV-2. antigen Saliva samples collected from more than 200 people up to 8 months after the virus-positive test.

The team found that the estimated half-life of the IgG response to the antigen was consistent with that previously reported for blood samples.

The results also show that the IgG response to two of the SARS-CoV-2 antigens persists in saliva for up to 8 months after the onset of symptoms.

“Saliva may serve as a blood substitute for large-scale monitoring of the humoral immune response for herd immunity monitoring and evaluation after SARS-CoV-2 infection and vaccination,” the researchers said. writing.

The preprinted version of the research treatise is medRxiv* Servers and articles have been peer reviewed.

Robust technology is needed to evaluate herd immunity to SARS-CoV-2

Robust methods for large-scale tracking of antibody responses after vaccination against SARS-CoV-2 infection or virus are important for accurate monitoring and evaluation of herd immunity.

Heaney et al. Previously developed and validated a multiplex bead-based immunoassay to detect antibody responses to three SARS-CoV-2 antigens in saliva. This assay measures IgG responses specific for the nucleocapsid protein, which is involved in the packaging of the viral genome. Spike protein (Required for host cell binding), and spike receptor binding domain (RBD) – main target Neutralizing antibody After infection or vaccination.

What was included in the current study?

Currently, researchers have collected 531 samples from 341 individuals within 8 months of testing SARS-CoV-2 PCR positive to assess the persistence of IgG responses to the antigen. This assay was applied to saliva samples.

Heaney et al. Assume that the endurance of antigen-specific IgG in saliva is at least 6 months and comparable to that reported in blood.

The team found that antigen-specific antibody levels peaked about 30 days after the onset of symptoms, after which 268 saliva samples from 237 individuals were assessed for IgG disruption.

Estimates of half-life of salivary IgG were similar to those reported in blood

The estimated IgG half-life was 64 days for nucleocapsid protein, 100 days for RBD, and 148 days for peplomer.

Researchers state that these half-life estimates for salivary IgG are comparable to those previously reported for plasma IgG. 67 days for nucleocapsid protein, 83 days for RBD, 140 days for spikes.

The majority of saliva samples from individuals who develop COVID-19 are specific for nucleocapsid protein (92%), RBD (95%), and spikes (93%) within 1-6 months of onset of symptoms. It was positive for IgG.

The proportion of saliva samples that were positive for these IgGs between 6 and 8 months after onset of symptoms was 32% for nucleocapsid protein, 68% for RBD, and 59% for spikes.

“These results show that SARS-COV-2 RBD and spiked IgG persist in saliva for up to 8 months after the onset of symptoms,” the team wrote.

When saliva samples were tested for all three antigen-specific IgG combinations, was the positive rate for SARS-CoV-2 specific IgG 98% 1-6 months after onset of symptoms and 6-8 post-onset? It was 73% in a month.

Heaney et al. Found that the saliva of most people with COVID-19 was positive for SARS-CoV-2 specific IgG up to 8 months after the onset of symptoms, and IgG against multiple SARS-CoV-2 antigens. It states that it shows that the answer can be incorporated. Improves the sensitivity of saliva-based antibody tests.

Time course of SARS-CoV-2 specific IgG reaction in saliva.  (A) Log10 median fluorescence intensity (MFI) of SARS-CoV-2 specific IgG response to nucleocapsid (N), receptor binding domain (RBD), spike (S), and Σ[S/CO] Medium value

Time course of SARS-CoV-2 specific IgG reaction in saliva. (A) Log10 median fluorescence intensity (MFI) of SARS-CoV-2 specific IgG response to nucleocapsid (N), receptor binding domain (RBD), spike (S), and Σ[S/CO] Value of n = 531 saliva samples (from n = 341 COVID-19 cases) over time. The solid black line represents temporal dynamics (estimated by the less spline). The dashed blue line represents the half-life (t1 / 2) and estimated gradient of the 95% confidence interval using the linear fit model (237 saliva samples n = 268). The gray dashed line indicates the cutoff value. The orange and gray white circles represent saliva samples that are classified as positive or negative, respectively. (B) A heat map detailing the proportion of saliva samples classified as positive by the number of days after onset of symptoms. caution. Log10 data is displayed on all plots. Σ[S/CO], The sum of the signals up to the cutoff. NAC, Native Antigen Company; Gen, GenScript; Sino, Sino Biological.

Findings support the use of saliva-based tests for large-scale surveillance

“Overall, these results support the usefulness of saliva as an accurate, non-invasive alternative to blood for longitudinal SARS-CoV-2 antibody testing and large-scale surveillance,” Heaney said. Said the team.

“Ideally, this analysis will be repeated with a large longitudinal sample set when it becomes available,” they advise.

*Important Notices

medRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.

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