Elsevier

Vaccine

Volume 28, Issue 20, 30 April 2010, Pages 3511-3515
Vaccine

Short communication
Decreased antibody titers and booster responses in tick-borne encephalitis vaccinees aged 50–90 years

https://doi.org/10.1016/j.vaccine.2010.03.024Get rights and content

Abstract

Because of decreased immune functions of older people booster intervals of 3 years – instead of 5 – are recommended for tick-borne encephalitis (TBE) vaccinations for persons ≥60 years in Austria. So far, no comparative data on the immune-responsiveness of the age group 50–59 years are available. We therefore investigated the antibody titers and booster responses (in ELISA and neutralization assays) for the age groups 50–59, 60–69, and >69 years in comparison to a control group below 30 years. The age group 50–59 years displayed the same decreased antibody response, also characteristic for persons 60 years and older. Although antibody concentrations were lower after 5–7 years compared to 3–4 year intervals, antibodies were still detectable and could be sufficiently increased by booster shots in the vast majority of persons. Our results clearly indicate that the responsiveness of the immune system to vaccination is already impaired at the age of 50.

Introduction

Tick-borne encephalitis virus (TBEV), a flavivirus belonging to the family Flaviviridae is endemic in parts of Europe and Asia and is transmitted mainly by the ticks Ixodes ricinus and Ixodes persulcatus [1]. Over the last years the incidence of TBE increased and endemic areas, where TBE-transmitting ticks are found, expanded [2]. The disease is characterized by a biphasic course. During the viremic phase uncharacteristic, influenza-like symptoms occur, which last for approximately 1 week. After an asymptomatic period of several days, 20–30% of infected persons experience CNS symptoms, such as meningitis or meningoencephalitis. 0.5–1% of TBE cases are fatal and permanent neurological sequelae are frequently observed. In Europe, approximately 3000 cases of disease following TBEV infection are recorded annually [3]. Vaccination with a purified, formalin-inactivated whole-virus vaccine is highly efficient to prevent disease [4], [5] and vaccination is recommended in endemic areas [6]. After a primary series of three vaccine doses booster vaccinations are recommended at varying intervals in different countries. Titers of vaccine-induced TBEV-specific antibodies are generally lower in the elderly [7], [8]. Previous work from our group demonstrated that the percentage of individuals older than 60 years with antibody concentrations not considered being protective increases with time since the last booster shot. In contrast, protection is >98% in young adults for at least 5 years after vaccination [7]. Since 2004, booster intervals of 5 years are recommended for persons under 60 years of age in Austria, whereas elderly persons should be vaccinated every 3 years.

Vaccination recommendations for senior citizens usually address persons above the age of 60 [9]. Some vaccinations however, such as against Herpes zoster and influenza, are recommended for persons older than 50 years in some countries. These recommendations take into consideration that immune functions, such as the output of naïve T cells from the thymus decrease dramatically between the age of 40 and 50 [10], [11]. Shortening of TBE-booster intervals to 3 years for individuals aged 50–60 years have therefore recently been discussed in Austria. Presently, there is no information on antibody concentrations before and after TBE-vaccination in persons between 50 and 60 years of age. We therefore analyzed IgG concentrations and neutralizing antibody titers against TBEV prior to and after booster vaccination for three groups of older adults (50–59, 60–69 and >69 years), and for a young control group of <30 years. At the same time we compared antibody concentrations in persons older than 59 years who had had the last booster vaccination either 3–4 or 5–7 years ago and compared their response to re-vaccination.

Section snippets

Participants of the study

Vaccination against TBE was administered to 79 healthy volunteers using an inactivated whole-virus vaccine (FSME-Immun® 0.5 ml, Baxter). Persons with malignancies, acute diseases or advanced stages of severe chronic diseases as well as persons under immunosuppressive therapy were excluded form the study. Four age groups were defined (<30: n = 14, median age 25, range 20–29 years; 50–59: n = 12, median age 58.5, range 51–59 years; 60–69: n = 22, median age 65; range 60–69 years; >69: n = 32, median age

Comparison of TBEV-specific antibody concentrations in different age groups prior to and after booster vaccination

Pre-vaccination antibody concentrations were determined in persons of all age groups (Fig. 1A and C). IgG antibody concentrations as well as neutralizing antibody titers were highest in the young control group, but significantly lower in all other age groups. Notably, there was no difference between individuals aged 50–59 years compared to older groups. All participants received a booster vaccination with TBE vaccine. Post-vaccination IgG antibody concentrations and neutralizing antibody titers

Discussion

Characteristic age-related changes of the immune system termed immunosenescence contribute to increased incidence and severity of infectious diseases [14] and decreased efficacy of vaccination in the elderly. It has been demonstrated in many studies that antibody titers are lower in the elderly compared to young adults after vaccination against influenza [15], hepatitis A and B [16], diphtheria, pertussis [17] and also TBE [18]. In addition, antibody titers against TBE and tetanus decline fast

Acknowledgement

We thank Baxter AG, Vienna, Austria for financial support of this study.

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