The discussion revolves around the lack of swelling at the injection site after an antibiotic shot, with participants exploring potential reasons for this observation. It is suggested that the absence of swelling could indicate that an infection did not develop immediately due to residual antibiotics preventing bacterial growth. Another possibility mentioned is that the injection site may have been scratched later, allowing bacteria to enter. Participants clarify that antibiotic shots typically do not cause swelling unless there is sensitivity to the antibiotic or its carrier. The conversation also touches on the distinction between antibiotics and vaccines, emphasizing that vaccines are intended to prevent infections and may cause mild swelling, while antibiotics treat existing infections. Concerns about tuberculosis testing and the implications of swelling at the injection site are also discussed, with explanations provided for terms like "immunocompromised individuals," "immunosuppressants," and "autoimmune diseases." Overall, the thread highlights the importance of understanding the differences between various medical interventions and the body's responses to them.