The duration of adverse reactions after MMR vaccination is about 7-14 days, and the incidence of adverse reactions generally decreases significantly after 14 days. The most common adverse reactions to MMR vaccine are redness, swelling, pain, and tenderness at the site of vaccination, which mostly appear within 24 hours after vaccination and disappear in 2-3 days; fever commonly occurs 7-12 days after vaccination, and the body temperature can be >39.0℃ for 1-2 days; relatively rare adverse reactions include skin rash, mumps, enlarged lymph nodes, and arthralgia, which are mostly seen in 7-14 days after vaccination. The relatively rare adverse reactions include rash, mumps, swelling of lymph nodes, joint pain, etc., which are mostly seen 7-14 days after vaccination. Therefore, after 14 days of MMR vaccination, post-vaccination adverse reactions are no longer likely to occur. If your child develops recurrent fever or rash after vaccination, consult a doctor.