Hi. Thank you for your post, and that’s a great question. Your doctor is correct that the virus in the flu shot is inactive, so it can't cause the flu itself. However, you're right to trust your instincts—vaccines do trigger an immune response, which can sometimes cause mild side effects like fatigue or body aches. While it’s uncommon for the flu shot to directly cause a COPD flare-up, it’s possible that your body’s immune response could coincide with other factors, leading to symptoms. It might just be a coincidence, but it’s always good to monitor how you're feeling and discuss any concerns with your doctor, as you have.Sometimes, as I can attest from my own asthma experience, it can be difficult to pinpoint what exactly triggers a flare-up. It's normal to speculate—I'm guilty of that myself—and my doctor has disagreed with me on occasion too (but that doesn't mean he's right lol). Regardless of what caused your flare-up, did your doctor offer any recommendations to help you feel better? John. community moderator.