Robust Antibody and T Cell Responses in COVID-19 Patients Six Months After Infection

Determining the longevity of natural immunity after SARS-CoV-2 infection is critical for understanding immune protection and optimizing vaccine design. Over six months have been passed since the emergence of COVID-19 in China. We evaluated humoral and cellular responses in 418 patients six months after infection. 95.9% and 98.1% of the patients maintained SARS-CoV-2-specific IgG and neutralizing antibodies. All severe patients were positive for IgG and neutralizing antibodies and had significantly higher titers than mild and moderate patients as well as asymptomatic individuals. The patients had a more robust SARS-CoV-2-specific CD4+ T cell response than CD8+ T cells six months after infection. Unexpectedly, sustained immune activation was observed, which displayed as the evaluated proinflammatory monocytes, non-classical NK cells, CD4+ Treg cells, and activated CD4+ T cells. Our findings indicate that SARS-CoV-2 gives rise to persisting and robust protective immunity, which provides a promising sign for prevention from reinfection and vaccination strategy. Funding: This work was supported by grants from the Natural Science Foundation of China (81773494 to M.J.M.), the National Major Project for Control and Prevention of Infectious Disease of China (2017ZX10303401-006 to M.J.M.), the Special National Project on Investigation of Basic Resources of China (2019FY101502 to M.J.M.). Conflict of Interest: The authors declare no competing interests. Ethical Approval: All patients provided written informed consent. The study was conducted following the Declaration of Helsinki, and the Institutional Review Board of the Academy of Military Medical Sciences approved the study protocol (IRB number: AF/SC-08/02.46).