Performance of SARS COV-2 IgG Anti-N as an Independent Marker of Exposure to SARS COV-2 in an Unvaccinated West African Population

Abstract

Determination of previous SARS-COV-2 infection is hampered by the absence of a standardized test. The marker used to assess previous exposure is IgG antibody to the nucleocapsid (IgG anti-N), although it is known to wane quickly from peripheral blood. The accuracies of seven antibody tests (virus neutralization test, IgG anti-N, IgG anti-spike [anti-S], IgG anti–receptor binding domain [anti-RBD], IgG anti-N + anti-RBD, IgG anti-N + anti-S, and IgG anti-S + anti-RBD), either singly or in combination, were evaluated on 502 cryopreserved serum samples collected before the COVID-19 vaccination rollout in Kumasi, Ghana. The accuracy of each index test was measured using a composite reference standard based on a combination of neutralization test and IgG anti-N antibody tests. According to the composite reference, 262 participants were previously exposed; the most sensitive test was the virus neutralization test, with 95.4% sensitivity (95% CI: 93.6–97.3), followed by 79.0% for IgG anti-N + anti-S (95% CI: 76.3–83.3). The most specific tests were virus neutralization and IgG anti-N, both with 100% specificity. Viral neutralization and IgG anti-N + anti-S were the overall most accurate tests, with specificity/sensitivity of 100/95.2% and 79.0/92.1%, respectively. Our findings indicate that IgG anti-N alone is an inadequate marker of prior exposure to SARS COV-2 in this population. Virus neutralization assay appears to be the most accurate assay in discerning prior infection. A combination of IgG anti-N and IgG anti-S is also accurate and suited for assessment of SARS COV-2 exposure in low-resource settings.

Subclinical SARS-CoV-2 Infections and Endemic Human Coronavirus Immunity Shape SARS-CoV-2 Saliva Antibody Responses

“…While serum anti-SCV2 N is often positive shortly after infection, the sensitivity of anti-SCV2 N IgG for diagnosing prior infection is highly variable (52% - 100%) 49,50 and its half-life post-infection is short, with one study estimating it to be only 35 days. 51 In this study, we utilized saliva anti-SCV2 N IgG as a marker for possible prior infection.…”

West African pre-pandemic cross-reactive antibody and cellular responses against SARS-CoV-2

“…In the past, we have used LFn to study T cell responses against several viruses, including HIV, Ebola, Zika, dengue, and SARS-CoV-2. 22–24,18 In our SARS-CoV-2 study of Nigerian HCWs and individuals from the general population, among individuals with SARS-CoV-2 N-only antibodies prior to vaccination, suggestive of prior exposure to hCoV, 81.8% (9/11) had T cell responses to SARS-CoV-2 N. These results provided further evidence that individuals who were previously exposed to hCoVs could have cross-reactive cellular responses against SARS-CoV-2.…”

“…Pseudotype virus neutralization assay was performed on Hela-ACE2 cells using SARS-CoV-2 spike pseudotype virus (PV) expressing luciferase as previously described. 23,24 Briefly, dried plasma spots were eluted and heat inactivated at 54°C for 1 hour, 25 and incubated with PVs at 37°C for 1 hour prior to addition of Hela-ACE2 cells. The plasma dilution/virus mix was incubated for 48 hours in a 5% CO2 environment at 37°C, and luminescence was measured using the Bright-Glo Luciferase assay system (Promega UK, United Kingdom).…”