A Cochrane review [Abstract] 1 included 11 trials with a total of 8 184 participants (6 586 adults and 1 598 children). Different versions of three types of TBE vaccines were tested (IPVE, FSME-IMMUN, and Encepur). No trials reported on cases of clinical TBE, but all reported on antibody titre (seroconversion). All the vaccines gave seroconversion rates of over 87%. There were frequent reports of systemic and local adverse effects, none of which were severe.
A meta-analysis 2 assessed the cross-subtype immunogenicity elicited by the currently available Western vaccines based on the European subtype. 14 RCTs were included into the qualitative and 4 into the quantitative analysis. Completed immunization course of 3 doses of both Western vaccines (FSME-IMMUN and Encepur) determined very high seroconversion/seropositivity rates against both Far Eastern and Siberian subtypes among previously flavivirus-naive subjects. Pooled analysis of randomized controlled trials on head-to-head comparison of immunogenicity of Western and Russian TBE vaccines did not reveal differences in seroconversion rates against Far Eastern isolates in either hemagglutination inhibition (RR 0.98, p=0.83) or enzyme-linked immunosorbent (RR 0.95, p=0.44) assays after 2 vaccine doses.
A commercially funded study 3 evaluated TBE antibody persistence after 3-5 years in children (aged 5-15 years): 2 groups previously primed with 3 doses of Encepur Children; and 2 groups previously primed with 2 doses of FSME-IMMUN followed by a third dose of Encepur. In the Encepur groups (full series), protective neutralization titers of HASH(0x304aee0)10 were detected in 98-100% of children up to 5 years after their last primary vaccination. In contrast, only 65-70% subjects in the FSME-IMMUN groups (mixed series) displayed titers HASH(0x304aee0)10 after 3 years.
Comment: The quality of evidence is downgraded by limitations in study quality (inadequate or unclear allocation concealment).
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