Maikova et al.
The ability of inactivated vaccines based on far eastern TBEV strains to induce humoral immune response in originally seropositive and seronegative recipients.
J. Med. Virol., in press, https://doi.org/10.1002/jmv.25316
While TBE vaccines produced in western Europe are based on the Western subtype (TBE-Eu), Russian and Chinese TBE vaccines are based on the Far Eastern subtype (TBE-FE). In Russia, all TBE virus subtypes are circulating, including the Siberian subtype (TBE-Sib). So far, no data exist on the immune response to Russian vaccines based on TBE-FE strains in individuals with pre-existing TBE antibodies due to natural infection by TBE-Sib. In the publication discussed, a clinical study has been carried out in originally seropositive and seronegative individuals living in a region where TBE-Sib virus is endemic (Sverdlovsk region). TBE vaccines used were Tick-E-Vac and EnceVir and cohorts were immunized twice with an interval of 30 days (standard scheme, SS) or 14 days, respectively (emergent scheme, ES). Immune response was evaluated by a 50% plaque reduction neutralization test (PRNT50) and seroconversion rates (SCRs).
Prior to the first immunization, 36% of the sera were positive to TBE-FE strain Sofjin and 8.9% of negative sera were positive for TBE-FE strain Ekaterinburg.
All vaccinees had protecting antibodies after two immunizations independent of the vaccination scheme and vaccines used. There was no statistical difference in the immune response regarding gender and age and between healthy persons and those with underlying chronic diseases. Vaccinees with a higher body mass index had a lower immune response after the first immunization. There was no difference in postvaccinal reactions in originally seronegative and seropositive vaccinees. One month after the first injection, originally seropositive vaccinees had had higher TBE antibodies compared to the seronegative group. Thirty days after the second injection, both groups showed a similar immune response.