Protective antibody titer for patients vaccinated against tickborne encephalitis virus

Two series of experiments (in vivo and in vitro) were performed to determine protective level of antibodies to tickborne encephalitis virus (TBEV). We considered, basing on the data of neutralization tests (one TBEV doze (3 lg TCID50) with different titers of specific IgG antibodies (from 1:6400 to 1:12.5)) that antibody titer 1:400 in enzymelinked immunosorbent assay (ELISA) and 1:20 in neutralization test (NT) is a minimal threshold of protective level, and 1:100 – a lower threshold of immunological memory. During the second series of experiments on neutralization of different TBEV titers (from 1 to 8 lg TCID50) with immunoglobulin (antibody titers 1:400 and 1:3200) we obtained the additional evidence that high IgG titers (1:3200) actively neutralized TBEV, and antibody titer 1:400 was the lower threshold of protection. This characteristic was used to assess an immunological effectiveness of vaccine Encepur® adult. After three years of a full vaccination course we observed high values of a specific immunity, and after five years, in half of the cases revaccination was required.