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US Population May Have More COVID-19 Immunity Than Previously Thought

June 2021 — According to a research article published online in the June 22, 2021 issue of Science Translational Medicine, data from a sero-surveillance study analyzing blood samples gathered from participants across the United States during the COVID-19 pandemic, suggest a higher level of infection-induced immunity exists in the US population than previously predicted.

The findings outlined in the article are the result of a nationwide COVID-19 "Sero-Survey" that involved investigators from multiple research centers including the NIBIB, NIAID, NCATS, and FNLCR within the National Institutes of Health (NIH), as well as the University of Pittsburgh and the University of Alabama at Birmingham. The investigators hypothesized that asymptomatic SARS-CoV-2 infection and delayed implementation of diagnostics had hindered our understanding of actual viral prevalence rates in the United States and elsewhere. Their study was aimed at providing a truer number of undiagnosed COVID-19 cases in the US.

The article's authors report that they analyzed seropositivity in 9,089 adults in the United States who had not been diagnosed with COVID-19. Individuals with characteristics that reflected the US population (n = 27,716) were selected by quota sampling from 462,949 volunteers. A total of 11,382 participants were enrolled in the study. Participants provided medical, geographic, demographic, and socioeconomic information, as well as dried blood samples they self-collected at home using Mitra® devices in Mitra® Collection Kits from Neoteryx. These microsampling kits contained visual instructions on the self-sampling process, as well as bandages, gauze, lancets, and four 20 μl Mitra microsampling devices for a total collection of 80 μl of whole blood. Remote participants using the Mitra devices submitted their blood microsamples by mail.

Some study participants opted for in-person blood draws performed by study staff using traditional venipuncture at the NIH Clinical Center phlebotomy lab. In those cases, 18 ml of blood was collected in a serum separator and whole blood tube. The majority (88.7%) of samples were collected between May and July 2020. Once received in the laboratory, serum samples were processed, while the dried microsamples that had been collected remotely were stored dry at -80°C until elution and analysis.

The participants' blood samples were processed using ELISA to measure seropositivity (IgG and IgM antibodies against SARS-CoV-2 spike protein and the spike protein receptor binding domain). The overall weighted undiagnosed seropositivity estimate was 4.6% (95% CI: 2.6-6.5%) with race, age, sex, ethnicity, and urban/rural subgroup estimates ranging from 1.1% to 14.2%. The researchers found that the highest seropositivity estimates were in African American participants, younger, female, and Hispanic participants, and residents of urban centers.

The data indicate that for every diagnosed case of COVID-19, there were 4.8 undiagnosed SARS-CoV-2 infections. This suggests that an estimated total of 16.8 million infections were undiagnosed by mid-July 2020 in the United States. From these data, one can infer that a higher level of infection-induced immunity exists in the US population today than previously predicted.

This is curated content. For details, please refer to the original article.
Science Translational Medicine 22 Jun 2021:
DOI: 10.1126/scitranslmed.abh3826

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