What causes some animal to hibernate?

Some animals require to hibernate to reduce their body temperature and slowing their metabolism rate for a variety of reasons. Sometimes the food become very scarce to find and an animal would find it hard to survive the harsh weather without hibernating. Many animals hibernate for a long time until the weather becomes suitable for them to search and find food. Sometimes the outside temperature may become very low and without hibernating the animal will die. These situations have increased the need for hibernation among different kind of animals.

No, when getting the flu vaccine no drugs should be being takin at the time.