it is a very safe vaccination with very little or even no side-effect. my daughter took it when she was 15 months, everything went ok. my doctor recommended me to do it because it can help fight against chicken pox, even if the baby is infected, only about 10% pox (e.g. a kid has chicken pox without taking this vaccination previously, will have over 100 poxes over the body, then, the kid with this vaccination will only have about 10 poxes.)
so , i recommend your baby to take that especially she is now schooling
If I am not wrong, the injection costs about HK$400.
The doctor did not say which season is better, he only said baby at 15 month is the ideal time for this vaccination because no other vaccination during that time and also the baby will be more out-going after one year old.