The hard lump after vaccination is mostly considered to be caused by the irritation of the injected drug on the tissue at the injection site, which can generally be eliminated by itself in about 1-2 weeks. Preventive vaccine is an antigenic substance or protein, which will produce certain stimulation reaction to the body, especially some children may have local hard lumps, slight pain or swelling, and may be accompanied by mild fever, usually about 1-2 weeks can be eliminated on its own, no need to take drugs to deal with. If other discomfort or the above symptoms persist, you should promptly visit a hospital for examination to clarify the cause and take appropriate measures. In addition, after vaccination, patients should pay attention to rest, drink more water, and eat a light and nutritious diet. At the same time, avoid getting wet until the needle hole crusts recover, and do not repeatedly touch the lump with your hands to prevent secondary stimulation and aggravation of local symptoms.