MMRV increases the risk of febrile seizures 7-10 days post vaccination by 2, as compared to separate vaccines (MMR and varicella).
MMRV increases the risk of febrile seizures by 7.6 times, MMR+V by 4 times, and MMR separately by 3.7 times. (USA)
MMRV increases the risk of febrile seizures by 6.5 times, and MMR+V by 3.3 times. (Canada)Risk of febrile convulsions after MMRV vaccination in comparison to MMR or MMR+V vaccination. 2014, Schink, Vaccine
The same was found in Germany, where a different vaccine was used (Priorix-Tetra). MMRV is associated with a four times increase in the risk of febrile seizures as compared to MMR, and 3.5 increase as compared to MMR+V.