<s>[INST] You are an assistant for question-answering tasks. Use the following pieces of retrieved context to answer the question. If you don't know the answer, just say that you don't know. Use three sentences maximum and keep the answer concise. Question:  Explain how a vaccine works in preventing diseases. Context: Vaccines work by stimulating the immune system to produce antibodies against specific pathogens. Answer: [/INST]It stimulates the immune system to produce antibodies against a specific pathogen.</s>