Short-term, mild reactions to immunizations are common. Immunizations that may cause a fever include:

• Diphtheria, tetanus, acellular pertussis (DTaP) or diphtheria, pertussis, tetanus (DPT). Babies can have a fever of up to 104°F (40°C) within 2 to 3 hours of getting the DTaP or DPT shot. Children may be fussy and have other mild symptoms such as poor appetite, sleepiness, or redness and swelling at the shot site for a few days.
• Measles, mumps, and rubella (MMR). The shot site may become red, swollen, hard, and slightly warm within the first 24 to 48 hours. Fever also may occur 1 to 2 weeks after the shot. A mild rash may develop up to 3 weeks after the shot.