Tolerability of modified tick-borne encephalitis vaccine FSME-IMMUN "NEW" in children: results of post-marketing surveillance.

A new, highly purified, inactivated tick-borne encephalitis (TBE) vaccine FSME-IMMUN "NEW" has been developed by Baxter using a production virus seed derived from chick embryo cells instead of mouse brain. In clinical trials, the vaccine was shown to be highly immunogenic and well tolerated in adults and children. Following licensure in 2001, the tolerability of half the adult dose of FSME-IMMUN "NEW" (1.2 microg antigen/0.25 ml) was investigated in a post-marketing surveillance in 1899 children aged 6 months to 12 years. Rectal body temperature was measured daily for 3 days after the first vaccination. An overall fever rate of 20.3% (95% CI=18.5; 22%) was observed, which was mostly mild in nature (>38.0 to <or=39.0 degrees C) with only 0.3% (95% CI=0.1; 0.6%) severe cases reported. The highest fever rates were reported in February and March (when febrile illnesses are common) and in the 1-3 years age group (63% of the total surveillance population). These results demonstrated that, in routine medical practice, FSME-IMMUN "NEW" vaccine at a dose of 1.2 microg antigen/0.25 ml is safe for the first vaccination in children.