This study investigates the correlates of protection against SARS-CoV-2 in rhesus macaques, focusing on the role of humoral and cellular immunity. The researchers found that adoptive transfer of purified IgG from convalescent macaques protected naive recipient macaques against SARS-CoV-2 challenge in a dose-dependent manner. Depletion of CD8+ T cells in convalescent macaques partially abrogated the protective efficacy of natural immunity, suggesting that cellular immunity is important, especially when antibody responses are waning or suboptimal. The study also demonstrated that relatively low antibody titres are sufficient for protection, and that cellular immune responses can contribute to protection if antibody responses are insufficient. Additionally, the findings suggest that convalescent plasma may be effective in treating SARS-CoV-2 infection, but only when high serum antibody titres are present. These results have implications for the development of vaccines and immune-based therapeutic agents.This study investigates the correlates of protection against SARS-CoV-2 in rhesus macaques, focusing on the role of humoral and cellular immunity. The researchers found that adoptive transfer of purified IgG from convalescent macaques protected naive recipient macaques against SARS-CoV-2 challenge in a dose-dependent manner. Depletion of CD8+ T cells in convalescent macaques partially abrogated the protective efficacy of natural immunity, suggesting that cellular immunity is important, especially when antibody responses are waning or suboptimal. The study also demonstrated that relatively low antibody titres are sufficient for protection, and that cellular immune responses can contribute to protection if antibody responses are insufficient. Additionally, the findings suggest that convalescent plasma may be effective in treating SARS-CoV-2 infection, but only when high serum antibody titres are present. These results have implications for the development of vaccines and immune-based therapeutic agents.