A new analysis of antibody and B cell responses in 44 people who received either the Pfizer or Moderna mRNA SARS-CoV-2 mRNA vaccines shows that only one dose may be needed for previously infected patients who have since recovered. The study also supported that two doses is optimal to induce strong antibody and B cell responses in patients who are immunologically naïve for SARS-CoV-2, and antibodies induced by the vaccination could protect against the more infectious and deadly South African variant. The results build on an increasing body of research suggesting that people previously infected with SARS-CoV-2 may only require one dose of mRNA vaccination for optimal immune responses, including new correlations with SARS-CoV-2-specific B cell responses in these patients. Rishi Goel and colleagues studied the antibody and B cell responses in the blood of 33 SARS-CoV-2-naïve patients and 11 patients previously infected with the virus at multiple time points before, during, and after vaccination. Consistent with previous findings, they confirmed that the mRNA vaccines induced antibodies that could neutralize the D614C and B.1.351 variants. These responses peaked one week after the second vaccine dose in naïve patients but peaked two weeks after the first dose in recovered patients, with similar patterns in B cell responses for both groups. Older patients had lower antibody and B cell responses after the second dose, and the generation of new antibody responses relied on SARS-CoV-2-specific B cells in all ages. Thus, Goel et al. confirm previous findings on antibody responses to SARS-CoV-2 mRNA vaccination, while expanding on the importance of B cell responses.