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Chapter 14: Prevention

vaccination and the age of the vaccinee, a A switch from Encepur to FSME-IMMUN for
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sufficient booster response was induced if at the 3 vaccination of the rapid immuniza-
least 2 or 3 primary vaccinations were tion schedule (1-7-21), as well as a switch
previously administered. 37,38 In addition, between first and second vaccination in the
similar results have been seen with Encepur, conventional schedule for FSME- IMMUN as
given as a catch-up vaccination after primary well as for Encepur should be considered
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or primary + booster vaccination. only under exceptional circumstances, as
these schedules are not licensed.
Vaccine interchangeability
Correlates of protection
In general, it is preferred that the same
vaccine brand is used for the complete Neutralizing antibodies directed against the
primary immunization series. However, in protein E represent the most important
order to not interrupt a vaccination series in mechanism of protection against TBEV, not
case of unavailability of a certain vaccine, only after natural infection but also after
the immunization series can be completed vaccination, even if antibody responses in
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with a different brand of TBE vaccine. both cases differ. According to the World
Several studies confirmed that FSME- Health Organization (WHO), in the absence of
IMMUN and Encepur can be safely a formal correlate of protection for TBE
interchanged for the third vaccination in the vaccines, these neutralizing antibodies can be
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context of the conventional primary used as a surrogate marker for immunity.
immunization of adults and children, as well Unfortunately, there is no generally accepted,
as for subsequent booster vaccina- standardized neutralization test nor any
tions. 11,15,23 In two studies – one in adults international reference reagents. In general, a
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and one in children aged 12 years and titer ≥1:10 is considered seroprotective;
younger - FSME-IMMUN was administered however, in the context of some vaccine
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as the 3 dose of the primary schedule after licensure studies, titers of ≥1:2 were accepted
two doses of Encepur; 11,15 in a third as a correlate for a significant immune
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pediatric study Encepur was given for the response. Neutralization assays as used in
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3 dose after two doses of FSME-IMMUN. various studies to determine seroprotection
after vaccination differed to a large extent:
A review describing 3 studies in which their sensitivity differed as well as different
Encepur was given as a booster after a test protocols were used, which makes a
complete primary immunization with FSME- comparison of results difficult. There is only
IMMUN (with or without booster) and one occasion of directly comparable TBE
further 3 studies in which Encepur or FSME- antibody test results with standardized serum
IMMUN was given for the third vaccination samples available and even in this study
after two doses of the respective other different NT test results were shown.
brand in the context of the conventional Moreover, detection of virus-neutralizing
schedule come to the same conclusion, antibodies in vitro was never correlated with
irrespective of the somewhat differing serum antibody concentration in vivo
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immunogenicity results. These differences, necessary to achieve solid protection in a
as mentioned several times throughout this subject.
chapter, are primarily due to the different
test systems used – utilizing a homologous ELISA results are not suitable as reliable
or heterologous TBE virus strain. surrogate markers for neutralizing anti-bodies
due to cross-reactivity with other flaviviruses

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