My baby will have her vaccine tomorrow. What can I do to prevent her from getting fever?

There are some mothers who boil 1 or 2 slices of "pao sheng/yang sheng AKA short american ginseng" in water and feed 1 or 2 spoonfuls to the baby before their vaccination. They say it does help to prevent fever. When my 3 month old went for her vaccination, I didn't take any particular precaution and she didn't get a fever after her 5 in 1, rotavirus and pneumococcal vaccinations. I believe it is because she is exclusively breastfed. Barley water might help as well. That said, I wouldn't recommend feeding anything but milk to a baby below 6 months. So just be prepared to sponge your baby if she develops a fever.