The baby after vaccination redness and swelling with hard lumps is the adverse reaction of the vaccine, but also does not exclude mosquito bites and other factors may be. If the baby has just completed the vaccination, there is a localized redness, swelling and hardness at the vaccination site, it is mainly considered to be an adverse reaction to the vaccine. Some babies may be allergic to the components of the vaccine, may appear in the vaccination site localized similar performance, belong to the normal range of adverse reactions. However, it cannot be ruled out that self-factors, such as mosquito bites, can also lead to the appearance of redness, swelling and hard nodules. Can also be accompanied by pain, itching and other symptoms. Therefore, we need to pay attention to timely observation, as long as there is no significant aggravation, then generally can be relieved by themselves. If it continues to grow, then you need to seek medical attention.