In patients with allogeneic stem cell transplants (alloSCT) and autologous (autoSCT) recipients, the immune system is impaired and therefore, these patients have an increased risk to acquire severe infections.

A clinical study has been carried out in Sweden in patients after alloSCT (n=51) or autoSCT (n=53), and the aim to investigate the feasibility, side effects, and humoral response of four doses of TBE vaccine (FSME-Immun®, based on Neudörfl strain) administered to these patients starting nine months post-transplant. The patients had a median age of 57 years, and in Sweden it is recommended to give four instead of three injections during the primary vaccination course in individuals aged at least 50 years. The control group was younger (median 39 years of age) and received three vaccine doses. For determination of IgG antibodies, an ELISA was used with a TBE antigen based on strain K23 and values of at least 12 U/ml were considered seropositive.

The results showed that the vaccine induced a robust antibody level increase after auto- and alloSCT. 79% of all patients had antibody levels above the presumed protective limit after three injections compared to 100% in the healthy control group after three injections. The latter group had significantly higher GMTs in the last serum sample (142.8) compared to patients (37.8). In most patients, mild reactions, mostly local pain, and swelling were reported.

The optimal time for many vaccinations after alloSCT is yet not clearly defined and many vaccinations are recommended to start at six months after transplant. The durability of TBE vaccination in these patients is not known.

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