Does the common cold only infect people during the winter?

No: The common cold can and does infect people year round (just ask any floridian). Cold viruses tend to be most active in the winter when people are more likely to be inside and close together and when the temperature is more conducive to viral reproduction, but plently of people get colds in the summer.

No: The common cold can occur year round but there is a higher frequency of colds in the winter months for several reasons: 1) more time is spent indoors, 2) we tend to close our windows in the winter resulting in more recirculated air, 3) more close contact with others (since 85% of respiratory infections are passed through hand-to-hand contact.