A liquid adsorbed pediatric TBE vaccine (Tick-E.Vac) based on the Far Eastern (FE) virus subtype, strain Sofjin, has been developed by the Chumakov Federal Scientific Center. This vaccine is licensed for individuals under 16 years of age and two doses are intramuscularly applied with an interval from 1 to 7 months (conventional scheme, CS) or 14 days (rapid scheme, RS). Subsequent boosters are recommended every 3 years. In a monocentric, randomized, double-blinded, controlled clinical trial, the reactogenicity and immunogenicity of this vaccine was compared in children and adolescents aged 1 to 16 years to FSME IMMUN Junior, which is based on the European (EU) subtype, strain Neudörfl. The study was carried out in Yekaterinburg, the Sverdlovsk region, where most TBE cases are caused by the Siberian (Sib) subtype of TBE virus. A total of 212 children were eligible for the study and were found seronegative prior to the vaccination. 152 participants would be vaccinated according to the CS scheme and 60 according to the RS scheme. However, 40 subjects refused to participate in this study before or after the second injection and were thus excluded from the study. Serum samples were collected on day 0, and 17 children (11.6%) had TBE specific antibodies at a titer of at least 10 measured by PRNT50, and this group was separately studied.
Local and systemic reactions reported in children were mild or moderate, usually occurred 1 to 2 days after vaccination and lasted no more than 3 to 4 days. The incidence of these reactions was statistically lower after the second dose and did not differ between the Tick-E-Vac and the FSME-IMMUN group. Both vaccines were highly immunogenic with seroprotection rates of 100% and 95%, respectively on day 30 after the second dose. Seroprotection rate was significantly lower on day 14 after the administration of the second dose using the RS scheme (50 to 63%) (compared to at least 90% in adults; data from another study). On day 30, there was no difference between the CS and RS scheme, but there are yet no data available on the long-term antibody persistence using the RS scheme. No higher reactogenicity was observed in the group of vaccinees who were sero-positive prior to the first injection.