Objectives: Data comparing the immunogenicity of Sputnik-V and Sinopharm vaccines in seropositive and seronegative groups are lacking. We compared the immunogenicity of Sputnik-V (Gam-COVID-Vac) and Sinopharm (BBIBP-CorV) vaccines in seronegative and seropositive groups. Methods: In total, 60 adults participated the study. The immune response after vaccination was assessed using enzyme immunoassay. IgG levels were measured in all participants at 3 time points: before vaccination, 42 days after the first vaccine dose, and 6 months after the first vaccine dose. The results of the SARS-CoV-2 antibody test were quantified according to the WHO First International Standard and expressed in international units (BAU per mL). Results: The study participants were divided into 2 groups: 30 people (50%) were vaccinated with Sputnik-V (Gam-COVID-Vac) and 30 people (50%) were vaccinated with Sinopharm (BBIBP-CorV). The groups had no difference in sex composition. The highest antibody levels were observed 42 days after vaccination in both the seronegative group (P = .006) and the seropositive group (P < .001). At 6 months after vaccination, the IgG value declined much farther among the seronegative group (P = .003) compared to those who had recovered from COVID-19 before vaccination. However, the “hybrid immunity” generated by the Sputnik-V vaccine had greater strength and duration (P < .001). Conclusions: This study showed that IgG levels in vaccinated individuals who previously recovered from SARS-CoV-2 infection (“hybrid immunity”) were higher than in SARS-CoV-2–naïve individuals. In a comparative part of the study, the Sputnik-V vaccine had greater strength and duration of immune response across the 6-month observation period (P < .001).