This is a summary, written by members of the CITF Secretariat, of:

Grunau B, Tom J, Asamoah-Boaheng M, O’Brien SF, Drews SJ, Sediqi S, Lavoie PM, Barakauskas V, Goldfarb DM, Sensitivity of the Elecsys Nucleocapsid Assay for the Detection of Preceding SARS-CoV-2 InfectionsOpen Forum Infectious Diseases, 2022, ofac349, doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, led by Drs. Brian Grunau, David Goldfarb, and Pascal Lavoie (University of British Columbia), and Sheila O’Brien and Steven Drews of Canadian Blood Services, and published in Open Forum Infectious Diseases, tested the sensitivity of the Roche anti-SARS-CoV-2 nucleocapsid assay. The authors addressed the question of whether the sensitivity of nucleocapsid assays is compromised in vaccinated populations, potentially due to less vigorous antibody responses. It found that the assay was equally sensitive regardless of an individual’s vaccination status and this held true if the participant was infected pre-Omicron or during the Omicron era.

The Elecsys anti-SARS-CoV-2 nucleocapsid assay has 89% sensitivity in identifying the presence of SARS-CoV-2 infections that had occurred 14 to 607 days prior to the collection of blood. This research is part of the COVID-19 Occupational Risks, Seroprevalence and Immunity among Paramedics (CORSIP) project.

Emerging data had questioned whether the sensitivity of nucleocapsid assays is compromised in vaccinated populations, potentially due to lower antibody responses. Additionally, sensitivity of the assay in the Omicron era is unknown and may be affected by nucleocapsid mutations. This study demonstrated that the Elecsys nucleocapsid assay showed 89% sensitivitySensitivity is a metric defining a test’s capacity to correctly identify people that are infected with SARS-CoV-2 when a test is positive. For example, a test with a sensitivity of 89% will, on average, correctly identify 89 people in every 100 who are truly infected with SARS-CoV-2. for identifying preceding SARS-CoV-2 infections in vaccinated and unvaccinated participants over an observation period of 607 days, which spanned SARS-CoV-2 wild-type to Omicron time periods.

Key findings :

  • Overall, the median COVID-19-to-blood collection interval was 63 days. Of the 205 participants that provided a blood sample ≥14 days post-diagnosis of SARS-CoV2, 182 had anti-N levels above the threshold value, which is the value at which a test is considered reactive or For vaccinated participants, 161/177 had a reactive testIn the Elecsys anti-SARS-CoV-2 nucleocapsid assay, a reactive test or “reactive assay” indicates the presence of anti-nucleocapsid antibodies. (sensitivity – 91%); while for the unvaccinated participants, 19/24 had a reactive test (sensitivity – 79%).
  • For the 91 cases in the Omicron era, the median COVID-19 infection-to-blood collection interval was 31 days. 84/91 participants had a reactive nucleocapsid assay with a sensitivity of 92%. Of the vaccinated participants, 80/87 had a reactive test (sensitivity- 92%), and of the unvaccinated participants, 2/2 had a reactive test (sensitivity – 100%).
  • For the 113 cases in the pre-Omicron era, the median COVID-19 infection to blood collection interval was 147 days. 97/113 participants had a reactive nucleocapsid assay, with a sensitivity of 92%. Of the vaccinated participants, 80/89 had a reactive test (sensitivity- 90%), and of the unvaccinated participants, 17/22 had a reactive test (sensitivity – 77%).

As of April 8, 2022, CORSIP had 3241 participants, of whom 420 (13%) reported having COVID-19. Of these, 205 participants provided a blood sample ≥14 days post-diagnosis. The COVID-19 tests were done between December 2020- January 1, 2022. 133 (53%) cases occurred pre-Omicron, 1 (0.49%) case occurred between the two time periods, and 91 (44%) occurred during the Omicron era. COVID-19 diagnostics by rapid antigen testing occurred in 48 (23%) cases and by PCR in 157 (77%).