Correlates of nucleocapsid antibodies and a combination of spike and nucleocapsid antibodies against protection of SARS-CoV-2 infection during Omicron XBB.1.16 and EG.5 predominant wave

BackgroundThe role of nucleocapsid (N) antibodies and their combination with spike (S) antibodies against SARS-CoV-2 reinfection remains unclear. We aimed to examine the association between N antibodies, a combination of N and S antibodies, and protection against SARS-CoV-2 reinfection. MethodsWe conducted a prospective cohort study among staff at a national medical research center in Tokyo and followed them for the incidence of SARS-CoV-2 infection between June and September 2023 (Omicron XBB.1.16/EG.5 predominant wave). At baseline, participants donated blood samples to measure N-and S-specific antibodies in assays from three companies (Roche, Abbott, and Sysmex). Cox regression was used to estimate the hazard ratio (HR) and protection (1-HR*100) against subsequent SARS-CoV-2 infection across these antibody levels. FindingsOf the 2549 staff included in the analysis, 237 SARS-CoV-2 infections were identified during follow-up. Among participants with previous infection, higher pre-reinfection N antibodies were associated with a lower risk of reinfection even after adjusting S antibody levels (P for trend<0.01). Estimation of the protection matrix for N and S antibodies yielded that high levels in both N and S antibodies conferred robust protection (>90%) against subsequent infection. In addition, a pattern of low pre-reinfection N antibodies but high vaccine-enhanced S antibodies showed high protection (>80%). InterpretationPre-reinfection N antibody levels correlated with protection against reinfection, independent of S antibodies. If the N antibodies were low, vaccine-boosted S antibodies could enhance the reinfection protection. FundingNational Center for Global Health and Medicine and Japan Health Research Promotion Bureau Research Fund. Research in context Evidence before this studyWe searched published and preprinted literature with the following keywords: "COVID-19," "SARS-CoV-2," "nucleocapsid," "spike," "antibody," "protection," and "reinfection." We found few prospective or case-control studies examining the association between pre-reinfection anti-SARS-CoV-2 nucleocapsid (N) antibody levels and risk of SARS-CoV-2 reinfection; in particular, no studies were conducted for adults among Omicron-dominant phases. We also found no studies that examined the role of a combination of anti-spike (S) and anti-N antibodies in protection against SARS-CoV-2 infection. Added value of this studyThis study first revealed that pre-reinfection anti-N antibody levels correlated with protection against reinfection during the Omicron XBB.1.16 and EG.5 predominant waves even after adjusting S antibody levels. Further, we first estimated the protection matrix by combining anti-N and S antibody levels and showed that both high levels in N and S conferred robust protection (>90%). Vaccine-induced higher S antibody levels were associated with higher protection among previously infected individuals with low levels of N antibodies. Implications of all the available evidenceThe prolonged COVID-19 pandemic has resulted in diverse immune characteristics across individuals due to varying timing of infection and doses and timing of vaccination, making it challenging to decide the timing of additional vaccination. Our results suggest the utility of assessing both N and S antibody levels for considering the timing of additional vaccination for those with a history of COVID-19. If the N antibody level was low due to waning over time, additional vaccination enhances S antibodies and might improve the protection against reinfection.