Tick-borne Encephalitis Vaccine Failures: A 10-year Retrospective Study Supporting the Rationale for Adding an Extra Priming Dose in Individuals Starting at Age 50 Years.

Karin E Hansson,Helena H Askling,Anja Rosdahl,Mona Insulander,Lars Lindquist,Sirkka Vene,Sara Gredmark-Russ

doi:10.1093/cid/ciz176

Abstract

BackgroundSouthern Sweden is endemic for tick-borne encephalitis (TBE), with Stockholm County as one of the high-risk areas. Our aim in this study was to describe cases of vaccine failures and to optimize future vaccination recommendations.MethodsPatients with TBE were identified in the notification database at the Department of Communicable Disease Control and Prevention in Stockholm County during 2006–2015. Vaccine failure was defined as TBE despite adherence to the recommended vaccination schedule with at least 2 doses. Clinical data were extracted from medical records.ResultsA total of 1004 TBE cases were identified, 53 (5%) were defined as vaccine failures. In this latter group, the median age was 62 years (6–83). Forty-three (81%) patients were aged >50 years and 2 were children. Approximately half of the patients had comorbidities, with diseases affecting the immune system accounting for 26% of all cases. Vaccine failures following the third or fourth vaccine dose accounted for 36 (68%) of the patients. Severe and moderate TBE disease affected 81% of the cases.ConclusionsTo our knowledge, this is the largest documented cohort of TBE vaccine failures. Vaccine failure after 5 TBE vaccine doses is rare. Our data provide rationale for adding an extra priming dose to those aged ≥50 years.

Highlights

Southern Sweden is endemic for tick-borne encephalitis (TBE), with Stockholm County as one of the high-risk areas
TBE is endemic in 27 European countries [3], with the highest annual incidence rate (5–18.6/100 000) in the Czech Republic, the Baltic countries, and Slovenia [4]
TBE virus is a flavivirus, and the hard tick Ixodes ricinus is the principal vector for the European TBE virus subtype, the main cause of European TBE cases [1, 2]

Summary

Methods

Patients with TBE were identified in the notification database at the Department of Communicable Disease Control and Prevention in Stockholm County during 2006–2015. Cases were identified in the national notification database (SmiNet) of the regional Department of Communicable Disease Control and Prevention. TBE was defined according to the national notification definition [34] and in agreement with the European Centre for Disease Prevention and Control’s criteria [35] as symptoms and/or signs of meningitis or meningoencephalitis and 1 of the following laboratory findings: TBE-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) in sera or specific IgM in the cerebrospinal fluid, seroconversion in paired sera over time, or detection of TBE-RNA in a clinical specimen. Patients diagnosed with TBE who had previously been vaccinated according to the recommended vaccine schedule with at least 2 doses of vaccine were defined as vaccine failures (Figure 1). Additional ELISAs and neutralization tests were performed at the Public Health Agency for 51 and 49 patients, respectively, as previously described [18]

Results

Discussion

Conclusion