A study published in *Cell* reveals that individuals who had asymptomatic or mild COVID-19 infections still possess robust T cell immunity, which may protect against severe disease. The research team analyzed T cell responses in unexposed individuals, family members exposed to infected individuals, and those with mild or severe COVID-19. They found that acute-phase T cells were highly activated and correlated with disease severity, while convalescent-phase T cells were polyfunctional and exhibited a stem-like memory phenotype. Importantly, T cells were detectable in antibody-seronegative individuals, suggesting that natural exposure or infection may prevent recurrent severe episodes of COVID-19. The study highlights the importance of T cell immunity in long-term protection against SARS-CoV-2, and suggests that even those with mild or asymptomatic infections may have strong immune responses that could help prevent severe disease. The findings indicate that T cell immunity is a key factor in immune protection against SARS-CoV-2, and that natural exposure or infection may provide long-lasting protection.A study published in *Cell* reveals that individuals who had asymptomatic or mild COVID-19 infections still possess robust T cell immunity, which may protect against severe disease. The research team analyzed T cell responses in unexposed individuals, family members exposed to infected individuals, and those with mild or severe COVID-19. They found that acute-phase T cells were highly activated and correlated with disease severity, while convalescent-phase T cells were polyfunctional and exhibited a stem-like memory phenotype. Importantly, T cells were detectable in antibody-seronegative individuals, suggesting that natural exposure or infection may prevent recurrent severe episodes of COVID-19. The study highlights the importance of T cell immunity in long-term protection against SARS-CoV-2, and suggests that even those with mild or asymptomatic infections may have strong immune responses that could help prevent severe disease. The findings indicate that T cell immunity is a key factor in immune protection against SARS-CoV-2, and that natural exposure or infection may provide long-lasting protection.