We assessed the humoral immunity of 290 vaccinated persons against
tick-borne encephalitis (TBE). During the first year and 2 years after the primary three vaccinations the
antibodies to the Far Eastern subtype tick-borne encephalitis virus strain P-73 were detected by neutralization test after immunization with FSME-Immune Inject
vaccine (Baxter
Vaccine AG, Austria) in 88.2% and 78.1% vaccinated persons, respectively; with
Encepur((R)) Adult
vaccine (Novartis
Vaccines, Germany), in 100% and 100%; with the
vaccine of the Chumakov Institute of
Poliomyelitis and Viral Encephalitides RAMSci (Russia), in 100% and 94.1%; with EnceVir
vaccine (Russia), in 88.2% and 83.9%; and after combined vaccination, in 100% and 92.7%. The dynamics of the decrease in
IgG avidity index correlated with the changes of antibody titers determined by neutralization test. After the primary vaccination course, the titers of virus-
neutralizing antibodies were high (6.3-7.4 log(2)) when the avidity index of
IgG antibodies were 31% and more; thus, this level can be considered immunologically significant. Two years after the primary vaccination course, the
IgG avidity indexes of 60% and more can be regarded as significant on the background of the GMT decrease of virus-
neutralizing antibodies. These results allow us to recommend all four
vaccines for mass vaccination and an assay of
IgG avidity, along with neutralization test, for a more adequate assessment of the level of postvaccination immune response.