It is possible for an 18-month-old to have a fever after receiving the MMR vaccine, which is a normal reaction to the vaccine.
MMR vaccine is a triple vaccine that prevents measles, mumps, and rubella virus infections. Fever, swollen lymph nodes, skin rash and other vaccine reactions may occur after vaccination, but most of the reactions are mild and may resolve on their own in about 1~3 days. 18-month-olds may also develop fever after MMR vaccination.
If an 18-month-old child develops a fever after receiving MMR vaccination, he/she can first take physical cooling methods, such as warm water baths, applying antipyretic patches, and paying attention to drinking water appropriately. If physical cooling fails to control the temperature, oral antipyretic medications, such as ibuprofen and acetaminophen, may be given. If symptoms persist, go to the hospital for further treatment.