Natural immunity viral infections can be obtained by taking vitamins. Certain vitamins have been shown to reduce symptoms of the cold and flu.Vitamins can reduce the symptoms and duration of the flu and provide natural immunity from viral and bacterial infections. Research has shown that vitamins taken before a flu can build immunity and prevent the flu. Taken during the flu, vitamins can shorten the duration and also mitigate the symptoms and suffering. Many of these vitamins are available from readily available foods and some need to be added to the diet by supplements.