Swelling and pain in the arm after the third vaccination can be treated with localized warm compresses, and if it continues to worsen or is accompanied by pus, medical treatment is required. After the third vaccination, the swelling and pain of the arm at the vaccination site is an adverse reaction caused by the vaccine. Usually the degree is mild and will not affect normal work and life, you can apply local hot compresses to accelerate blood circulation and promote the swelling to subside. However, if the effect of hot compresses is not obvious, the swelling and pain continue to worsen, or accompanied by pus and other manifestations, the possibility of combined infection is greater. At this time, we need to consult a doctor in a timely manner, local tissue culture, blood tests, etc., to clarify the specific causative organisms, and then take antibiotics such as cefoperazone sulbactam sodium for treatment. Therefore, the degree of mild can continue to observe, self-management, if continue to aggravate the need to consult a doctor.