Some strains can cause only mild symptoms (like the common cold). Since allergies can sometimes make people feel as though they’re getting sick, allergies mainly cause itchy and watery eyes, a runny nose, congestion and sneezing. Your immune system is the greatest defense against the common cold. It usually affects your nose, throat, and lungs and can last from five to seven days. If you received a flu shot and still get the flu, your symptoms are generally milder than if you didn’t receive the flu shot.