Korean J healthc assoc Infect Control Prev.  2023 Jun;28(1):92-98. 10.14192/kjicp.2023.28.1.92.

The Difference in Anti-nucleocapsid Protein Antibody Responses Between Vaccinated and Unvaccinated Individuals After Asymptomatic, Mild, or Moderate COVID-19 Infection

• Kim JY
• Cha HH
• Kwon JS
• Cha JH
• Jang CY
• Lee HJ
• Lim SY
• Kim SH

• KMID: 2543139
• DOI: http://doi.org/10.14192/kjicp.2023.28.1.92

Abstract

Background
Anti-nucleocapsid protein IgG antibody (N-IgG) responses are not elicited by the current COVID-19 vaccines; therefore, these responses have been used to determine previous COVID-19 infections. However, data on whether COVID-19 vaccination affects the seroconversion of the N-IgG response are limited. This study aimed to compare the seropositivity of N-IgG responses in vaccinated individuals versus unvaccinated individuals with COVID-19 confirmed by polymerase chain reaction (PCR).
Methods
The study included healthcare workers (HCWs) and immunocompromised (IC) patients with liver or kidney transplants, regardless of their COVID-19 infection status, who have received COVID-19 vaccines (ChAdOx1, BNT162b2, or mRNA-1273) between March 2021 and December 2021. We also enrolled unvaccinated patients infected with COVID-19, who were asymptomatic or had mild or moderate symptoms. Anti-spike 1 protein IgG antibody (S1-IgG) and N-IgG responses were measured in plasma obtained from the participants.
Results
None of the 100 individuals (51 HCWs and 49 IC patients) without Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) infection demonstrated a positive N-IgG response. Among the patients with PCR-confirmed SARS-CoV-2 infection, the rate of N-IgG positivity was 93.5% (29/31) in the unvaccinated patients, which was significantly higher than that in the vaccinated HCWs (75.0% [39/52], P=0.04). The positive rate of N-IgG in vaccinated IC patients was numerically lower (60.0% [9/15]) than that in vaccinated HCWs; however, this difference was not statistically significant (P=0.33).
Conclusion
COVID-19 vaccination lowered the seroconversion rate of N-IgG in patients with COVID-19. Therefore, the estimate of SARS-CoV-2 infection based on the N-IgG response may underestimate the seroprevalence of SARS-CoV-2 infection in highly vaccinated populations.

Keyword

Anti-nucleocapsid protein antibody; COVID-19 infection; Seroconversion; Vaccination

Figure

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  Fig. 1 Timeline of vaccination and plasma samples collection and study flowchart diagram. (A) Intervals of vaccination, plasma collection and antibody measurement for healthcare workers (HCWs) and immunocompromised (IC) patients. (B) Study flowchart of HCWs and IC patients’ enrolment and results of antibody responses.

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