Page 453 - TBE_Book_V2_2019

Chapter 14: Prevention

(specifically antibodies resulting from capable of neutralizing heterologous TBEV
infection or vaccination). Moreover, the ELISA strains. 45
assay does not distinguish between antibodies
with low and high avidity, hence determining While it has been shown that an immun-
also antibodies without neutralizing capacity. ization with Encepur in subjects leaving in
Therefore, ELISA measurements are primarily regions with Far Eastern TBEV circulation
useful for screening purposes. The HI test, induced higher immune responses in
which has been broadly used in the past, is no originally seropositive as compared to
longer considered state of the art. seronegative individuals, similar data with
vaccines based on the Far Eastern TBEV
94
Cross-protection strains are limited.
Evidence exists that TBE vaccines protect not A recently published study found statistical
only against the homologous subtype, but also significant differences in the immune
against heterologous subtypes (European, response in subjects with pre‐existing
Siberian, and Far-Eastern TBEV subtypes). In immunity to the TBEV FE strain Sofjin or
vitro and in vivo studies have shown broad Siberian strain Ekaterinburg‐27‐11‐06 as
cross-neutralizing capacity of vaccine-induced compared to seronegative individuals, only
antibodies by either vaccine. 24,25,34,42,43 after the first vaccination with one of the two
Moreover, a recently published systematic Russian TBE vaccines (Tick‐E‐Vac based on FE
44
review supports robust cross-neutralization strain Sofjin and EnceVir based on FE strain
with the exception of 1 strain (TBEV-Fe P-69), 205). After the second dose, the difference
95
for which a significantly lower level of was insignificant
neutralization was determined. In contrast,
there is no evidence from human studies Antibody persistence, age, and duration of
43
(except against Omsk HF) that vaccine- immunity
induced TBEV antibodies provide cross-
protection against other flaviviruses. Up to the year 2004, 3-year booster intervals
were recommended for the 2 European TBE
vaccines. However, in 2004 and 2006 data
To overcome the problem of missing com-
parability data between immune responses to suggesting a longer seropersistence became
38,46
different TBEV strains, due to a poorly available. Since then, studies investigating
standardized methodology, a novel test the seropersistence after primary and booster
system that uses hybrid viruses was vaccinations with both European vaccines
16,19,47–49
have been conducted.
developed; this system allows an unbiased
head-to-head comparison of the humoral
The seropersistence of TBEV antibodies in 347
responses against different TBEVs from all 3 adults between the ages of 18 and 67 years
subtypes. Studies using this new technique was evaluated 2 and 3 years after completion
have found comparable vaccine-induced
of the primary vaccination, with the first 2
neutralizing titers against TBEVs of all doses being either FSME-IMMUN or Encepur.
subtypes, in sera of subjects who received 2
The third dose consisted of FSME-IMMUN for
doses of FSME IMMUN Junior, and somewhat all study subjects. Seropositivity rates of
50
reduced, but still protective, neutralization 96.8% and 95.4% were determined using NT 2
capacity against Omsk hemorrhagic fever and 3 years after the third dose of the primary
43
virus (OHFV). Another study found series, respectively. All subjects (100%)
differences in the ability of 2 European
achieved seropositivity after the subsequently
pediatric TBE vaccines to induce antibodies
administered first booster vaccination.

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