SARS-CoV-2 N protein and anti-spike serologies: insights into COVID-19 disease severity and mortality—a secondary analysis of the ACTIV-1 trial

Background: Understanding factors that predict progression to severe COVID-19 is critical. Antibodies targeting SARS-CoV-2 spike protein confer protection, while the N protein of SARS-CoV-2 plays roles in viral replication and immune dysfunction. This study explores the significance of N protein and anti-spike antibodies on disease severity, progression, and mortality. Objectives: To evaluate the relationship between SARS-CoV-2 N protein and anti-spike antibody levels with disease severity, clinical outcomes, and mortality in hospitalized patients with COVID-19. Design: A secondary analysis of serologic data from participants in the ACTIV-1 randomized clinical trial, which evaluated immunomodulators for the treatment of hospitalized patients with COVID-19. Methods: A subanalysis of the ACTIV-1 immune modulator trial was conducted. Samples collected at randomization were tested for N protein levels and anti-spike antibodies. Logistic regression and linear models were employed to examine the association between serological measures and clinical outcomes, including 28-day mortality as well as progression to high-flow nasal cannula (HFNC) and invasive mechanical ventilation (MV). Results: Among the 496 participants with detectable serum N protein, the median was 1143 ng/dL, and levels decreased from 2559 ng/dL in participants randomized at 6 days of symptom onset to 477.6 ng/dL at 11 days. Higher anti-spike antibody levels were seen as the days from symptom onset progressed or disease severity increased. Greater disease severity at randomization was associated with 28-day mortality, prolonged days of oxygenation, ventilation, hospitalization, and risk of new non-invasive ventilation, HFNC, MV, or extracorporeal membrane oxygenation use. N protein levels were associated with a higher risk of new non-invasive ventilation or HFNC use, longer oxygenation duration, and extended hospitalization. Anti-spike antibody serologies were not associated with clinical outcomes. Conclusion: N protein levels could provide insights into COVID-19 disease progression and prognosis. Further research is needed to explore the clinical implications of these findings to optimize patient care and enhance outcomes. Plain language summary Understanding COVID-19 severity: the role of viral proteins and antibodies COVID-19 severity can vary widely, and predicting who will develop severe disease is crucial for effective treatment. This study looks at two key components of the virus: the N protein, which helps the virus replicate, and anti-spike antibodies, which help the body fight off the virus. We studied blood samples from participants in a clinical trial to see how levels of these two components related to disease severity and outcomes, such as the need for advanced respiratory support or death. The study found that higher levels of the N protein were associated with more severe disease and worse outcomes, including a higher risk of requiring advanced respiratory support and longer hospital stays. On the other hand, anti-spike antibodies, which are typically seen as protective, did not show a clear relationship with the severity of illness or outcomes in this study. These findings suggest that the N protein might be a useful indicator for predicting how severe a person's COVID-19 illness might become, which could help doctors better manage and treat the disease. However, more research is needed to fully understand the role of these viral components in COVID-19 and how they can be used to improve patient care.