Post-marketing surveillance of immediate allergic reactions: polygeline-based versus polygeline-free pediatric TBE vaccine.

Scattered cases of immediate allergic reactions occurred in the nineties after widespread use of the original (polygeline-based) pediatric tick-borne encephalitis (TBE) vaccine and were reported to Pharmacovigilance, Chiron Vaccines. Although, still indicating a very rare frequency of about two cases per 100,000 doses sold, the benefit/risk assessment resulted in its withdrawal from the market in early 1998. An intensive evaluation revealed that polygeline used as a vaccine stabilizer was the most probable cause of the reported allergic reactions. Consequently, an improved pediatric TBE vaccine, free of polygeline and other protein-derived vaccine stabilizers, was developed. A post-marketing surveillance analysis covering the first two vaccination seasons after the introduction of this new pediatric TBE vaccine in early 2002 reveals a very low reporting rate of immediate allergic reactions post immunization (within the range as noted for other widely used vaccines for childhood immunization), i.e., 0.08-0.24 cases per 100,000 doses sold depending on case definition and medical assessment. In conclusion, this analysis provides post-marketing surveillance evidence that the change in the vaccine formulation, with regards to the potential risk of immediate allergic reactions, has led to an intended improvement in the vaccine's safety profile.