The appearance of a cold or flu is a sign of weak immunity.
Even if you are perfectly healthy and you have a strong immune system, you can become victims of viruses and a cold.However, a strong immune system will help make it easier to deal with common cold. Studies have shown that poor immunity and stress and contribute to worsening of symptoms.
Vitamin C will protect you from the cold.
Receiving vitamin C is not effective protection against cold. But receiving enough vitamin C before the onset of symptoms will shorten the duration of symptoms.