Sir my baby had vaccine on his shoulder on one and half month. there it has become a thick lump by swelling. this vaccine was given on 11th december 2021. he is 3 month old now. what should we do please help?

There may have been bleeding in the muscle or a bruise that is slowly resolving. An imaging study may be helpful if there is an Infection. Watch for signs of fever, redness and discharge.

These are often knotted muscle fibers that were injured by the jab. They can take 6-8 weeks to self heal and I have never seen a case that did not. A warm compress applied to the site can increase blood flow and speed healing. However, I would consider trying to keep it in place for a kid that age more trouble than its worth. I give most such jabs in the upper legs at that age (less problems)