Understanding the long-term maintenance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunity is critical for predicting protection against reinfection. In an age- and gender-matched cohort of 24 participants, the association of disease severity and early immune responses on the maintenance of humoral immunity 12 months post-infection is examined. All severely affected participants maintain a stable subset of SARS-CoV-2 receptor-binding domain (RBD)-specific memory B cells (MBCs) and good neutralizing antibody breadth against the majority of the variants of concern, including the Delta variant. Modeling these immune responses against vaccine efficacy data indicate a 45%–76% protection against symptomatic infection (variant dependent). Overall, these findings indicate durable humoral responses in most participants after infection, reasonable protection against reinfection, and implicate baseline antigen-specific CD4+ T cell responses as a predictor of maintenance of antibody neutralization breadth and RBD-specific MBC levels at 12 months post-infection. Display omitted •SARS-CoV-2-specific humoral immunity is sustained at 12 months post-infection•Severe disease is associated with more durable immune responses•Immune responses are equivalent to a vaccine protective efficacy of 45%–76%•Early CD4 T cell responses predict durable neutralization and memory B cells One year after SARS-CoV-2 infection, despite declining antibody titers, Balachandran et al. report a disease-severity-associated maintenance of antibody functions and memory B cell magnitudes. The convalescent serum could neutralize most VOCs, and the initial CD4 T cell levels predict the antibody neutralization breadth and memory B cell durability.