Influenza virus causes flu and other respiratory diseases. Our immune system protects us from infection causing microorganisms. We can prevent many types of diseases and health problems by strengtheing the immune system. Lack of sleep and stress are the main causes of poor immunity. You should sleep well. Learn to control stress. Include fruits and vegetables in your diet. Eat yogurt and nuts. Get Vitamin D through sun exposure. You can take Vitamin D supplements. Eat immunity-boosting foods like garlic. Do regular exercise and stretching. Maintain good hygiene by washing hands. Avoid bad habits like alcohol and smoking. Following are the top 9 ways to boost your immunity.