Page 455 - TBE_Book_V2_2019

Chapter 14: Prevention

which is hoped to further increase the vaccine The majority of these studies included
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coverage in the country. subjects who received their primary
vaccination series below the age of 50 years,
Based on the meanwhile available long-term which might have influenced the duration of
seropersistence data after the first booster a seropositivity and B-cell memory. 47,53
prolongation of the booster intervals appears Unfortunately, few data exist on primary
feasible, especially for the younger vaccination in individuals of more advanced
population. Primarily in countries with very age.
low vaccination coverage this could have a
positive effect. However, all data generated An observational study with FSME-IMMUN
with respect to this issue have limitations, and Encepur administered to previously
since the study participants were fully unvaccinated elderly subjects reported
immunocompetent, and therefore do not seropositivity rates of 95% and 80%, respect-
entirely represent an unselected population. tively, for subjects vaccinated with FSME-
Moreover, it is questionable if countries with IMMUN (as measured by the Immunozym and
very well-established vaccination programs Enzygnost ELISA Kits) and 65% and 80%,
and high vaccination uptake would benefit respectively, for subjects vaccinated with
from such an extension. Little clinical data Encepur (as measured by the Immunozym and
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exist on the seropersistence of TBE antibodies Enzygnost ELISA Kits).
after the 3rd dose of the primary immun-
ization. In one study investigating TBE This study illustrates not only the reduced
seropositivity 2 and 3 years after the third immune response after TBE vaccination seen
50
vaccination subjects aged 18-50 years in the elderly population, but it also gives
showed higher seropositivity rates (88.7% and evidence for dependence of serologic results
92.3%, after 2 and 3 years, respectively) than on the commercial ELISA test systems.
those aged 51-67 years (65.5% and 70.9% Unfortunately, this study was not evaluated
after 2 and 3 years, respectively), thus using NT. One study, which compared the
confirming the appropriateness of the existing primary immune response in older and
manufacturer recommendation for the younger subjects, showed that subjects
administration of the first booster dose 3 primed after the age of 50 years achieve not
years after completion of the primary series. only lower titers but also experience a more
There are no data on long-term sero- rapid decline of neutralizing antibodies as
persistence for the 2 Russian and the Chinese compared to subjects primed at a younger
vaccines. Twelve months after primary immun age. Of note, almost no difference in the
-ization, seropositivity rates of 72%, 87%, and booster response was found between the 3
77% were determined for EnceVir, TBE- older age groups: 50–59 years, 60–69 years,
Moscow, and the Chinese Vaccine, respective- and >69 years of age, indicating that
6
ly. responsiveness to vaccination is impaired
54
already by the age of 50.
Most of the studies conducted in elderly
individuals have shown consistently lower A relatively recent study investigated the
antibody concentrations compared with immune response to a conventional primary
younger age groups. 54-57 A cross-sectional immunization schedule with FSME-IMMUN in
study from the highly endemic Åland Islands previously unvaccinated subjects >70 years of
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found that age of the individual and number age. Four weeks after the second and third
of vaccine doses were the 2 most important vaccinations, 98.5% and 99.3% of subjects
factors for determining the immune response were seropositive (≥10) by NT, even if GMTs
to vaccination. 50,55 were generally lower. Although antibody

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