Boosting of the SARS-CoV-2-specific immune response after vaccination with single-dose Sputnik Light vaccine

Despite the measures taken worldwide, COVID-19 pandemic still progresses. While efficient antiviral drugs are not yet widely available, vaccination is the best option to control the infection rate. Although this option is obvious in case of COVID-19–naïve individuals, it is still unclear when individuals who have recovered from a previous SARS-CoV-2 infection should be vaccinated and whether the vaccination raises immune responses against the coronavirus and its novel variants. Here we measured the dynamics of the antibody and T-cell responses, as well as virus neutralizing activity (VNA) in serum against two SARS-CoV-2 variants, B.1.1.1 and B.1.617.2, among 84 individuals with different COVID-19 status who were vaccinated with Sputnik Light vaccine. We showed that vaccination of individuals previously exposed to the virus considerably boosts the existing immune response. In these individuals, RBD-specific IgG titers and VNA in serum were already elevated on the 7th day after vaccination, while COVID-19–naïve individuals developed the antibody response and VNA mainly 21 days post–vaccination. Additionally, we found a strong correlation between RBD-specific IgG titers and VNA in serum, and according to these data vaccination may be recommended if the RBD-specific IgG titers drop to 142.7 BAU/mL or below. In summary, the results of the study demonstrate that vaccination is beneficial both for COVID-19–naïve and recovered individuals, especially since it raises serum VNA against the B.1.617.2 variant – one of four the SARS-CoV-2 variants of concern.