Persistence of immunity to tick‐borne encephalitis after vaccination and natural infection

Abstract

Long-term persistence of immunity was assessed in 66 patients who had contracted tick-borne encephalitis (TBE) and in 126 subjects who had completed primary TBE immunization using a conventional three-dose schedule from 3 to 8 years earlier. Immunity was tested in the subjects stratified by age as follows: ≤40 years (N = 37); 41-60 years (N = 100); and over 60 years (N = 55). Antibody levels decreased significantly with increasing age in the vaccinated cohort by comparison with the individuals who had previously contracted TBE. Consistently higher geometric mean antibody levels were found in the patients infected naturally. When the vaccinated subjects were compared, subjects ≤40 years old had significantly higher antibody levels than either of the older groups. Analyzing immunity to TBE over time revealed a remarkable (50%) decline in seroprotection rates in the vaccinated group at 50 months of follow-up, while stable, high levels persisted in all subjects after natural TBE infection. In the vaccinees over 60 years old, the TBE antibody levels reached 60% at 60 months, and 20% at 70 months of follow-up; in contrast, in the 41-60-year-old group, the antibody levels remained high for 70 months, and then fell rapidly. For people aged <60 years old, booster doses are recommended every 5 years after the fourth dose of vaccine, which should be administered 3 years after primary immunization. In subjects aged 60 years or older, booster doses should be given every 3 years.

Factors Determining Immunological Response to Vaccination against Tick-Borne Encephalitis Virus in Older Individuals

“…From the questionnaires we acquired information regarding previous tick-borne infections, general health status, and vaccination status for TBE as well as for yellow fever and Japanese encephalitis (Appendix S1). We included 8 health-related factors from the questionnaires in the analysis that we considered might influence the immune response; previous TBE disease [22], vaccination against other flaviviruses (yellow fever or Japanese encephalitis) [38], ≥2 tick-bites during the previous 3 months [39], pet-ownership (dog or cat) [40], asthma [41], smoking [42], allergy [43], and diabetes [44]. If a study participant visited health care for a suspected tick-borne disease during the 3-month study period we also investigated their medical records.…”

“…Although age affects the quantitative antibody response, the quality of the antibodies appears unaffected by increased age [24]. In contrast to vaccination, individuals naturally infected with TBEV preserve high antibody titers throughout life [22]. Vaccine failures can occur in all ages, despite complete vaccination, but the majority of cases are among individuals over 50 years old [15], [25], [26].…”

Comparison of Four Serological Tests for Detecting Antibodies to Japanese Encephalitis Virus after Vaccination in Children

“…They found that all three tests detected antibodies at a maximum of 4 months after the last vaccine dose and that there was a good correlation between the antibody titers. Baldovin et al [20] investigated the persistence of TBEV antibodies in vaccinated ( n  = 126) and naturally infected ( n  = 66) groups. Blood samples from participants in the vaccinated and natural infection groups were sampled 3–8 years after the last immunization and 1.4–13.7 years after viral infection, respectively.…”

Epidemiological and Ecological Studies of Tick-borne Encephalitis Virus

“…Using a rapid schedule with the Encepur vaccine (days 0, 7, 21) in children has been shown to provide fast protection and stable antibody levels for at least 1 year [209]. The antibody response to TBEV vaccination declines with age [210][211][212][213][214][215][216], and older individuals are at higher risk of vaccine failures [189,200,217]. Both the European vaccines are considered safe to use and efficacious for individuals ≥1 years old by the WHO [201].…”