Sondén M,
et al. Fatal European subtype tick-borne encephalitis in a fully vaccinated immunocompetent child: a case report with viral sequencing. BMC Infect Dis. 2026;26:1048. doi:10.1186/s112879-026-13657-0.
A case report has analyzed in detail a severe tick-borne encephalitis (TBE) virus infection in a 9-year-old girl with a fatal outcome.
The clinical presentation was atypical, as the patient did not develop fever and lacked the typical biphasic course of illness. This atypical manifestation delayed diagnosis and appropriate medical management in the emergency department. The encephalitis progressed extremely rapidly, with signs of cerebral herniation evident before external ventricular drains were inserted on the sixth day after symptom onset. Such an aggressive course of TBE is uncommon for infections caused by the European subtype of TBE virus.
The child had completed a full primary vaccination series. However, 3.5 years had elapsed without administration of a booster dose (the first booster is recommended three years after the third dose of the primary vaccination series). The measured IgG levels during the central nervous system (CNS) phase of the disease likely represented a combination of vaccine-induced and infection-induced antibodies. No pre-illness serum samples were available; therefore, TBE antibody levels prior to infection could not be assessed. Testing for NS1 antibodies was positive.
The patient had no history of recurrent severe infections and tested negative for HIV. Furthermore, no evidence of immunodeficiency was identified through extensive genetic testing, including whole-genome sequencing.
The TBE virus genome was recovered from brain tissue obtained at autopsy. The strain was identified as belonging to the European subtype and was closely related to previously reported strains circulating in Sweden.
This case of atypical TBE virus infection highlights the importance of considering TBE in the differential diagnosis of headache and neurological symptoms in endemic areas, regardless of vaccination status.