Evaluation of vaccine Encepur® Adult for induction of human neutralizing antibodies against recent Far Eastern subtype strains of tick-borne encephalitis virus

We studied humoral immune response of 44 volunteers from Primorsky krai (Russia) immunized with the vaccine Encepur® Adult. Induction of the humoral response towards the recently isolated tick-borne encephalitis virus (TBEV) strains P-69, P-202, and P-73 was evaluated by neutralization test and enzyme immunoassay. These strains belong to Far Eastern TBEV subtype based on their genotype and antigenic structure but maintain significant genetic and antigenic variability. The average geometric titers of neutralizing antibodies to P-69, P-202, and P-73 strains were 1:28, 1:34, and 1:128, respectively. The percentage of volunteers with neutralizing antibodies to these strains after complete course immunization was 63.9, 97.6, and 95.5%, respectively. We concluded that Encepur® Adult vaccine induced pronounced humoral immune response towards genetically and antigenically heterogeneous strains of the Far Eastern TBEV subtype.