The main claim of the passage is that taking precautions such as getting the flu shot, practicing good hygiene and healthy habits, and washing hands frequently are important in staying well during the cold season. Some examples of supports for this claim include mentioning that flu shots are a first line of defense, that many places offer free shots, and that healthy eating and proper sleep also help prevent illness.
An example of a sentence in the second paragraph that contains an irrelevant detail is "The most common cold virus is the rhinovirus." This sentence, while informative, does not directly support the main claim and is not necessary in explaining the importance of washing hands frequently to avoid colds and flu.