Hansson et al.
Tick-borne encephalitis (TBE) vaccine failures: a ten-year retrospective study supporting the rationale for adding an extra priming dose in individuals from the age of 50 years.
Clin. Infect. Dis. 2019, in press, doi: 10.1093/cid/ciz176
In Sweden, the following standard primary immunization scheme for TBE vaccine is recommended: day 0, 1-2 months, 5-12 months, followed by a booster three years later. Further doses are recommended every five years, independent of the age of the vaccinee. For individuals of at least 60 years of age, an extra dose at month 3-4 is recommended for the primary vaccination course.
A retrospective study of all reported TBE cases in Stockholm county from 2006-2015 has been carried out with the aim to identify vaccine failures and their circumstances. A total of 1004 TBE cases have been notified, among which 53 (5%) were defined as vaccine failure. Most vaccine failures occurred in men (64%), 81% were older than 50 years of age, and the medium age was 62 years. 36% of the individuals had received 3 or 4 vaccine doses prior to the infection and 21% had received 5-9 doses. 68% fell ill following 3 or 4 doses of vaccine. All but one of the patients had started their vaccination after the age of 50 years, and none of the patients had received the recommended extra dose during the primary vaccination course. Half of the patients had comorbidities, and 15% were on immunosuppressive treatment. The authors conclude from their data that an extra dose for individuals over 50 years of age is warranted.