Schmitt et al.
TBE vaccination breakthrough cases – Does age matter?
Vaccines. 2021; 9(8):932. Doi:10.3390/vaccines9080932

TBE vaccines are highly effective in preventing TBE; however, vaccine failures (breakthrough infections) are sometimes reported.

An international team has analyzed the age distribution of vaccine failures (VF). In this study, VF was defined as a patient with reported TBE despite having received at least two doses of either FSME Immun or Encepur (both are inactivated whole virus vaccines based on the European subtype) at least two weeks prior to the onset of disease symptoms, and the last dose applied as recommended in the label. A systematic literature review has been carried out, supplemented by data from public health institutes, to identify the relative number of patients in Latvia, Sweden, and southern Germany (Bavaria and Baden-Wuerttemberg) younger or older than 50 years of age.

A total of 173 VF were identified in the three above mentioned countries with a mean age of 62, 55, and 40 years for Sweden, southern Germany, and Latvia, respectively. In Latvia, 65% of the patients were younger than 50 years of age, while in Germany 40% and in Sweden only 19% were younger than 50 years of age. The proportion of TBE cases in individuals younger or older than 50 years were similar in the three countries. However, the proportion of VF was different.

For Sweden – in contrast to Latvia and Germany – the proportion was disproportionally higher in the older age group.

The authors discussed various hypotheses for this phenomenon. The higher proportion of VF in older age groups observed in Sweden warrants further investigations.

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