BCG vaccination three years after the sudden redness and swelling, if only redness and swelling, can not be treated for the time being; if accompanied by other symptoms such as ulceration, it is recommended to go to the hospital for treatment. In general, about 2 weeks after BCG vaccination, redness and swelling will appear at the inoculation site, and the scab will disappear after 8~12 weeks. If redness and swelling appear locally at the vaccination site after three years, it may have nothing to do with the effect of the vaccine itself, and if the symptoms are mild or the range is small it is normal and can be left untreated for the time being. If there is redness and swelling at the site of vaccination, the redness and swelling are large in scope, or accompanied by pus, ulceration, fever and other symptoms, it may be caused by allergies, infections, etc., and it is recommended to go to the hospital for examination and treatment.