Hi, I had gone through your question and understand your concerns. I dont think this is a side effect of injection. This sounds to me more likely to be swollen lymph nodes. Swollen lymph nodes in neck area are commonly seen and in most cases if there are no other symptoms, it doesn’t indicate any disease. However if there are additional symptoms such as fever, rapid growth of node, cough, weight loss or excessive swelling then this may be something pathological and require treatment. In these cases it is most commonly cause by some sort of infection.The most common cause of swollen lymph nodes is an infection, particularly a viral infection, such as the common cold. Other possible causes of swollen lymph nodes include:Strep throat, Measles, Ear infections, Infected (abscessed) tooth, Mononucleosis. Mononucelosis is commonest along the young people and this should be ruled out first. Then it can be treated with antibiotics or other medications depending on established cause. He should drink more fluids, take ibuprofeum and rest as much as possible till symptoms persist. In doubtful cases, lymph nide biopsy can be taken but I don’t think this is necessary at this point. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health.