Yes, the flu can weaken the immune system. When you have the flu, your immune system is busy fighting off the influenza virus. This can temporarily weaken your body's defenses against other infections.   As a result, you become more susceptible to secondary infections, such as pneumonia, which can develop while your immune system is focused on combating the flu.   These secondary infections can be particularly perilous for individuals with compromised immune systems, as they may face greater challenges in fighting off these additional infections.   It is crucial for immunocompromised individuals to take extra precautions and seek prompt medical attention if they contract the flu to minimize the risk of secondary infections.