It is not guaranteed that a baby will develop a fever after their 2-month vaccine. Some babies may experience slight pain during the injection, but not all will experience a fever. If a fever does occur, it typically only lasts a few hours and does not usually require medical attention unless it persists for more than 48 hours or is accompanied by other concerning symptoms. It is actually beneficial for a child to develop a fever after a vaccination, as it indicates that the body is mounting an immune response. It is not recommended to give Tylenol before the vaccination to prevent a fever, as the inflammatory response that causes the fever is crucial for the vaccine to be effective. Overall, there is usually nothing to worry about regarding fever after a 2-month vaccine.