RESUMO
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-naive 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-naive 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-naive 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.
RESUMO
Rapid spread of COVID-19 pandemic made a substantial share of the world population immunised by SARS-CoV-2 antigens. Infection induces the development of virus-specific antibodies and T cells. Ample evidence on the antibody-mediated protection is contrasted by the elusive role of T cells in preventing infection. To explore the impact of T cells and to quantify the protective levels of the immune responses we conducted a large prospective study: 5,340 Moscow residents were evaluated for the antibody and cellular immune responses to SARS-CoV-2 and monitored for COVID-19 up to 300 days. The antibody and cellular responses were tightly interconnected, their magnitude inversely correlated with infection probability. Similar maximal level of protection was reached by individuals positive for both types of responses and by individuals with antibodies alone. Meanwhile, T cells in the absence of antibodies provided an intermediate level of protection. The real-world data on the protective effects of T cells have important implications for T cell immunology and development of the strategies to fight the pandemic.
