Page 456 - TBE_Book_V2_2019

Chapter 14: Prevention

concentrations are lower in the elderly, vaccinations in the past and therefore had
booster doses have been shown to sufficiently high numbers of TBE-specific effector memory
increase the antibody levels, indicating an T cells. Quantification of different T-cell
adequate immune memory response in the subpopulations (naïve, memory, and
elderly population as well. Moreover, 1 study suppressor T cells) before and 1 week after
showed that the quality of antibodies as booster vaccination showed a relative
measured by antibody avidity were intact decrease in regulatory T cells after vaccina-
59
despite the lower antibody titers. The tion. This is most likely due to an effector T-
findings described above underscore the cell expansion induced by the booster
importance of adhering to the recommended vaccination and not the result of a decrease in
63
schedules, including the 3-year booster the total number of regulatory T cells.
intervals in subjects age 60 years and older.
Moreover, in the region of Stockholm an Moreover, the investigators observed an
+
additional dose of the primary schedule is increase in the percentage of CD4 T cells
recommended for subjects older than 60 years combined with a slight relative decrease of
+
of age. Such an explicit recommendation how- CD8 T cells after intramuscular vaccination
ever does not exist in other countries and and a relative decrease of effector memory
+
existing epidemiological data do not support CD4 T cells after subcutaneous vaccination.
+
this recommendation. However, the observed changes in the CD4
+
and CD8 T-cell sub-populations were very
Cellular immunity small and had no influence on neutralizing
63
antibody titers. Whereas all these data were
Until recently little was known about the obtained after TBE booster immunization in
cellular immune response after TBE previously vaccinated individuals, data are
vaccination. Immunization with inactivated lacking on the cellular immune response in the
TBE vaccine has been reported to induce context of TBE primary vaccination.
+
primarily a CD4 T-cell response with a very
+
low induction of CD8 cells. 60,61 More recent Vaccine effectiveness
investigations of TBE ‘low- responders’ after
vaccination showed a positive correlation Austria is a highly endemic country for TBE
with humoral and cellular immune responses with a very long history of TBE immunization.
upon booster vaccination: high or low TBE Vaccination coverage has increased steadily
titers were associated with sufficient or lack since the 1970s, when the first TBE vaccine –
of Ag-specific T-cell proliferation, respective- FSME-Immun – was initially licensed.
62
ly. According to an investigation of the field
effectiveness of TBE vaccines in Austria during
Research published in 2016 reported on the the years 2000–2006, 88% of the Austrian
cellular immune response after a booster population has a history of TBE vaccination,
vaccination of FSME-IMMUN, administered by and 58% were vaccinated according to the
35
subcutaneous and intramuscular routes, licensed schedule. For the above-mentioned
revealing that interleukin-2 (IL-2), interferon period, when FSME-IMMUN comprised 90% to
(IFN) gamma, and interleukin-10 (IL-10) levels, 95% of the TBE vaccines administered in
produced upon antigen re-stimulation of Austria, an effectiveness of approximately 99%
peripheral blood mononuclear cells (PBMCs), was calculated for regularly vaccinated
63
were already elevated prior to vaccination. persons, with no statistically significant
35
This observation is in line with the fact that all difference between age groups. Not a single
study subjects had received multiple TBE case of TBE was recorded within the first year

451
458