Add green tea to your diet to prevent flu. Studies show that green tea prevents flu, when consumed regularly. Green tea catechins do two things: prevent infection and inhibit growth and reproduction of viruses. And, green tea catechins protect against any type of flu virus. The flu vaccine each year just protects against that year's most prevalent flu type. In addition, many studies show green tea catechins have the ability to kill or prevent other viruses and bacteria, for example, Salmonella, food poisoning, Candida, etc.