There is no one definitive answer to this question, as the timing will vary depending on your individual situation and chemotherapy treatment. However, it is generally safe to say that your immune system will start rebuilding back up within a few weeks after completing chemotherapy therapy.
This process may take longer if you have significant cancerous tumors or if you received high-dose chemo treatments.
Your immune system will also be working hard to eliminate any leftover cancer cells, which means that there could be some temporary side effects related to immunity such as fever, sweats, chills, and flu symptoms.
But overall, most people experience an improved sense of well-being once their body has recovered from undergoing cancer treatment.