Redness, swelling and hardening of the arm after vaccination is completely normal and is a normal local reaction to vaccination. After the vaccine enters the body, it begins to produce an immune response, and localized redness and swelling occurs, so don’t massage or squeeze it. If squeezed, part of the bacteria from the vaccinated wound will enter the inner layers of the skin and an inflammatory reaction or spreading of the redness and swelling will occur, leading to infection under the skin. Therefore, if there is no obvious redness or swelling, no fever in the whole body, and the spirit is good, there is no need to worry too much, and it will subside naturally after a few days. There are some vaccines, such as BCG vaccine, which will have localized suppuration and it is normal to leave a scar. Therefore, if there is redness, swelling, hardness, etc., do not touch raw water. After contact with raw water, use iodophor to sterilize the area locally, do not squeeze, and observe for a few more days.