TBE Vaccination Breakthrough Cases—Does Age Matter?

Abstract

Tick-borne encephalitis (TBE) vaccines are highly effective in preventing TBE and vaccine failures (VF) are rare events. In this study, we compared the age distribution of TBE cases and TBE VF in three endemic countries: Sweden, Southern Germany, and Latvia. While the age distribution of TBE cases was similar for those <50 years versus those ≥50 years in all three countries, in Sweden, a higher proportion of VF cases was ≥50 years, whereas most VF cases in Latvia were <50 years of age and more evenly distributed between those <50 years versus those ≥50 in Southern Germany. Here, theoretical explanations were provided, including differences in diagnostic practices, vaccine uptake between age groups, behavioral patterns and underlying medical conditions, as to why VF were generally older in Sweden than the other countries. There is no scientific rationale to give an extra priming dose of TBE vaccine to subjects ≥50 years of age.

Retrospective, matched case–control analysis of tickborne encephalitis vaccine effectiveness by booster interval, Switzerland 2006–2020

“…An additional limitation is that, while we found TBE VE appeared similar between age groups, as we matched cases and controls by age we were unable to directly compare VE values. While some studies have demonstrated reduced serological responses to TBE vaccination and increased vaccine breakthrough in older individuals,17 20 30 31 other work has shown vaccination breakthrough to be comparable between older and younger age groups, and that VE remains high even among those aged 60+ 32 33. Clarifying how TBE VE is impacted by age remains an important area warranting further study.…”

Vaccination against Tick-Borne Encephalitis (TBE) in Italy: Still a Long Way to Go

“…An association between age and vaccine breakthroughs was observed in a Swedish study. However, it is noteworthy that approximately half of the patients in whom vaccine failure was observed had comorbidities affecting the immune system, suggesting that other factors could explain the higher proportion of vaccine failure in subjects aged ≥50 years [61]. However, there is no evidence that an additional priming dose is of "immunological" or clinical benefit [61,62].…”

Recommendations to Improve Tick-Borne Encephalitis Surveillance and Vaccine Uptake in Europe

“…High field vaccine effectiveness, >90%, has been demonstrated in several settings and across all ages, including people ≥60 years old [ 24 , 25 ]. However, breakthrough TBE, despite vaccination, has been noted across Europe [ 26 , 27 ]. Some authors quote that these vaccine failures appear to occur more often in patients >50 years of age, possibly due to age-related weakening of the immune system, though the exact cause has not been elucidated [ 27 , 28 , 29 ].…”

“…However, breakthrough TBE, despite vaccination, has been noted across Europe [ 26 , 27 ]. Some authors quote that these vaccine failures appear to occur more often in patients >50 years of age, possibly due to age-related weakening of the immune system, though the exact cause has not been elucidated [ 27 , 28 , 29 ]. However, this is not generally accepted and recent studies do not confirm a higher vaccine failure rate in the elderly [ 23 ].…”