Kinetics of Antibody Response to Repeated Vaccination with Sputnik V: A Pilot Study with a Series of Five Cases.

Objectives: Widespread vaccination is considered as one of the best methods in combating any pandemic including COVID-19. Gam-COVID-Vac also known as Sputnik V, is one of the first vaccines that was registered in 74 countries and received an emergency approval for immunization. Monitoring anti-SARS-CoV-2 antibodies over time is essential for evaluation of post-vaccination humoral immune response.To date, there are only a limited number of clinical studies regarding the analysis of immune response after Sputnik V administration. It is of crucial importance to report independently on safety and efficiency of this vaccine with the aim to speed up the process of its final approval by the WHO.

Methods: Humoral immune response was monitored by seven immunoassays to analyze different classes of anti-SARS-CoV-2 Ig in five health workers after receiving the combined vector vaccination. This vaccine is based on two replication-deficient rAd26 and rAd5 viral vectors that carry the gene SARS-CoV-2 full-length glycoprotein S(rAd26-S and rAd5-S). Sputnik V was administered with a 21-day interval between the first and second dose. Venous blood was collected two hours before vaccination as a baseline, and then followed by 18 series up to 170-day post-vaccination.

Results: The participants in this study used a self-report form in which they noted their observations on safety at 72 h post-immunization. One participant reported mild side effects, such as muscle pain and fever, while the other four individuals had no noticeable complications. Seroconversion was detected in all individuals at 28 days of post-vaccination. Plateau of seropositivity has been achieved by 50th day of vaccination, while titer values decreased after 6 months.

Conclusion: This study provides some clinical data regarding the kinetics of antibody levels elicited after administration of heterologous rAd26-S and rAd5-S vaccine. Based on the preliminary data from this pilot study, it appears that Sputnik V vaccine generates a solid humoral immune response lasting at least 6 months after immunization.